yeah you are putting extra wear on the transmission, but really every street car out there is pretty much designed to have people doing normal downshifts, you could downshift normal for the whole life of your car and probably never see any real damage. but that doesnt mean that heel toeing is bad, if you can then why not?
and yeah it can definatly mess up the balance of the car if you do normal downshifting in the wrong way, you can still downshift smoothly without heel toeing, but it can take alot longer. and a sudden jerky downshift could be really bad in snow, and im guessing everyone here drives in snow alot.
so say your coming into a corner and have to downshift 2 gears and brake from 70mph to 40, in order to downshift smoothly without heel toeing, you have to let the clutch out very slow so you might end up having to finish the downshift while going into the corner, which you dont want, its almost always better to have your shifting done before the corner. where with heel toeing you could get your two downshifts done and have plenty of time left before you enter the corner, since your not having to be slow letting the clutch out.
or say your coming up to a corner in the snow that you hardly have to slow for but you need to be in a lower gear to power out of it, if you have to suddenly pop into a lower gear its going to unsettle the car pretty bad right before the corner. where if you were heel toeing or even just rev matching you get down to the lower gear without unsettling the car at all, and you can control the car with the throttle and brake.
but the biggest reason to heel toe especially in a racing situation, or even just fast driving is to not get lock up under braking, if you are braking at the limit of adhesion, then do a normal downshift its trying to slow the car down more when you are already at the limit, which will cause lockup. and the only way to prevent it is to be at say 90 percent of your braking potential, which is slower, to allow for that extra slowing through the downshift. where with heel toeing you can have constant braking pressure while downshifting, so you can be at 100% and remain at 100% the whole time.
and yeah its definatly a big no no to have the clutch in through a corner in racing. any coasting is bad, you want to be constantly slowing and accelerating, because its faster and you have more grip that way. braking and accelerating effects the balance of the car, giving weight to the front or back of the car, giving that part of the car more grip, and different corners, and different parts of the corner require grip at different parts of the car more than others. so say your going through a flat 90 degree corner, you might need to trail brake into the corner to get the car to rotate towards the apex, so your transfering all that weight to the front tires letting them turn in with more grip leaving the back with less grip which will alow the car to rotate slightly, and get aimed in the right direction. then you would have to roll back to power around or before the apex, slowly transfering that weight to the rear of the car giving the back more grip and allowing it to accelerate out, and slowly turning cornering grip into straight line grip giving you better exit speed. this is just a simple example, there might be corners where you want to accelerate through the whole thing to keep the weight in the rear of the car, or different combinations.
it may seem super unneccesary, but when you can understand it and use it right, it will make even your "fast" street driving, snow driving, avoiding accidents, or whatever ALOT better.
