Actually, leaving the throttle at 100% the whole time is a mistake, especially when you are in a 2-seater and you are flying to line your WSO up for some good shots. At max thrust, your WSO will not have enough time to effectively

1.) Establish a lock
2.) Maintain lock through the inevitable flares, spoofing the one shot that he is able to throw down
3.) Reaquire lock once the flares have cleared.

In the single-seat fighters and bombers, thrust management is also essential for a variety of reasons. For those jets capable of dropping bombs, the best approach vector for getting bombs on target is a near vertical dive. And again, going at max speed leaves little time to make adjustments to guide your bomb's trajectory against moving targets or, even more importantly, for when your're gunning down ground targets to clean them up after (or soften them up for) a bombing run. And it sounds strange, but when you're supressing AAA nests, slower is better for accuracy purposes. You want to make sure that you get all the bullets you can on that pinpoint, unmarked position (hopefully before they know you're comming and can react) or your goose is cooked; those suckers only need 2-3 square hits to wreck your day.

Also critical for any jet is thrust control when in a dogfight. When in a fighter and in persuit of a slower, more cumbersome bomber, leaving the throttle at 100% will guarantee that you will overshoot your target and he'll make an easy get away through the turns. Matching his speed allows to you put lots and lots of gunfire on his tail before he even knows you're there in most cases (the more cagey pilots check their six regularly) and allows you to stay on his tail once he starts evasive maneuvers. But by then you should have banged up his jet a fair deal and can clean him up with a couple missiles.

In truth, I rarely fly around the map at max thrust (what I like to think of as "military thrust") as I feel that going slower allows me to loiter around areas of the map that need my attention for longer periods of time and increases my situational awareness of what's happening above and below. I only open it up when I see another jet and need to gain a position on his six, or when I've spotted one on my six and need to shake him.

Mind you, when I say "slower" I don't mean setting the throttle to near stall-speeds, as that will get you killed. What you want is to find a comfort zone between stall speed (~350 KPH for most aircraft) and military thrust (~1000 KPH for the fighters without after burners) This allows you to boost up to max thrust quickly without consuming too much AB fuel or allow you to drop to lower energy flight for setting up clean bombing runs and return again to cruising speeds.

Moving on, your control scheme is also important. Some people are comfortable with the mouse and keyboard. I don't like it because you lose a great deal of control with that. Apart from the mouse and the mousewheel, all the rest of your control surfaces are actuated by buttons that are either 100% on or 100% off. This is a problem as it requires constant button management (or tapping) in order to make fine tuned flight adjustments. Unless you have the patience for that sort of thing, most people simply keep the buttons pressed until they they've maneuvered the aircraft to where they want it to be. Since they are operating their plane at 100% button values (max left, max right, up, down, etc. depending on how they mapped "wsad" and mouse controls), this makes their flight patterns very predictable; they'll always be flying within circles of equal turn radii.

The most successful pilots are the ones that are able to fine tune their flight controls such that no one evasive maneuver looks like the last. For that, the best choice is a joystick. But the good ones tend to be expensive and I find that they are less usefull for driving the ground vehicles. My personal selection is with the gamepad, particularly the PS2 mock-ups with 2 analogue sticks, as shown below:

The only drawback with that setup is that I have to button manage my left/right rolls with the two top buttons. It's not bad but I've been giving a lot of thought toward moving those controls down to the X-Y axis on the right analogue stick with thrust control. I could use the extra two buttons for other things (comm's channels) and it spares me the tapping and I don't lose any control with the thrust management either.

With the gamepad, I find I get the same level of control I would with my joystick and have an excellent ground vehicle control scheme without having to switch stuff around on my desk. It's far more comfortable to use and it sits on my lap when I'm not using it, or when driving a tank for instance. But I'm getting off topic with that so I'll stop there.

Adressing one of your earlier questions regarding the use of after burners. You see people tapping the ABs probably because they are near max thrust and don't need the burn a whole lot to regain energy lost in a turn. In BF2, the flight model is exactly realistic in a number of ways, mainly in that higher thrust/speed = a tighter turn radius (which is rather dubious). But that's a minor gripe of mine. Anyway, ABs are a precious resource and should not be wasted. Use them to boost your speed in carefull increments and always have enough left over to make a nice long boost when you've shaken your enemies and need to get out of Dodge in a real hurry. And on that note, the higher you are, the faster you'll go either on standard thrust or AB assited thrust. Keep in mind however, that aircraft lose control at ~750 meters (it's actually more like 800, but 750 is where I put my redline). Cross that threshold and your plane will spin out of control and more often than not into out of bounds material for a senesless death (a major irritation of mine - it's the stupidest limitation ever imposed in a game).