As an accredited photographer for the races perhaps I can answer this one!

It's all governed by light.  You need to be where it works for you, not against you.  During practice the light falls off sharply towards the end of the session, so you need to try and find a place where it stays with you as long as possible.  On very sunny days the light can be very contrasty so I tend to avoid places where deep shadows might be cast. 

You may also want to move between races, so you need somewhere you can escape from.  Professional camera gear can be very heavy too so that can limit where you can get if you have a lot of equipment to lug about.

Agreed, some people go to favourite spots each year - I'm guilty of that from time to time - but when you've got an editor depending on you to get results, you've got to make sure you have publishable shots to present.  Experimenting is all well and good if you have no pressure on you but if you try something a bit off piste and it doesn't work then the day's a bust.