I have no problems running foams (love the traction) but I prefer rubber tires.
The most overlooked point is that if you know what your doing and drive reasonably well and your on pace with your competition your foams will last a month. But if your testing set ups and practicing a lot trying to improve your lap times, you could easily burn through 2-3 sets of foams in less than a week.
Rubber tires can last 2 months and maybe longer. I wouldnt want to race 2 month old rubber tires in the main, but, they are still viable for practice. The same cant be said about 2 month old foams.
One could argue against practicing with the older rubber tires because they have lost their edge, but I've found that if the car is working o.k. with practice tires, it works even better with fresh tires.