RAM mac-pro than they need?

RAM holds information to be used immediately by your computer. It stands for Random Access Memory.

RAM allows your computer to gain access to data faster than if it were stored on a hard disk.

Picture a person juggling balls - those balls represent data information, and the juggler is RAM. The Juggler (RAM) is keeping the balls (data) actively available, so it can immediately be used by your software, as opposed to the balls (data) that are still in the Juggler's bag (hard disk).

The more RAM you have available to your computer, the more information it can have immediately available.

In Photoshop, for instance, more RAM means the ability to work with larger files quicker, because the data can be "juggled" or kept immediately available, rather than stored on a hard drive. More RAM will, in general, speed up access to information and data on your computer.

In your case, I think more RAM would probably help with Premiere and FCPX.

Hope this helps. From your question, it appears English is not your first language, so I hope I interpreted your question correctly.

If you have a 3,1 with only 8GB of ram and use Premiere, switch to the use of the CUDA cores if you have an Nvidia video card installed.