Isolation pads - how many ?

I am in the process of purchasing all of my components and various necessary cables and tweaks for a new system I am building for a new room which is being built. I have decided to go with Herbie's Audio Lab Tenderfeet under my components. However, I have seen two configurations of using 3 or sometimes 4 feet underneath each component. Is there a difference ? Can I get away with using 3 for each unit (meaning each amp, pre/pro, source player, power conditioner, and TV) ? What constitutes using 4 ? Thank you for your help / opinions.
the manufacturers tend to study how their equipment sounds with a variety of feet, and tend to use the ones that work the best.....don,t get any tweeks until you'e had a chance to get to know your stereo.
Most of the time, three feet work better than four.

Having said that, I agree with jrd that you would do well to test before committing every piece in your system to one footer.

If you look in Audiogon's archives under footers, isolation and tweaks, there are dozens of threads where members have posted their experience. Using that as a start point and doing a bit of experimentation, you will absolutely know what is best for your sound and you learn in the process.

Many of these items may be found used at Audiogon. Not a lot of risk if the item fails to please as it may be resold.
I have been trying suspension and isolation tweaks for over 15 years on many components. I have tried virtually every type mentioned in the threads. I have NEVER ecountered a situation where 4 feet sound better than 3, EVER.