does a partition with the OS and all other programs help the apps to run more efficent?
I assume you mean ONE partition for the OS and ANOTHER partition to store your programs.
In that case, the answer is NO, it isn't more efficient.
Here's why I partition my drive:
1. Multiple OSes. My main HD has the following OSes: DOS, Windows XP for general use (has lots of background applications running), Windows XP for Games (just has bare minimum drivers for my gaming hardware and almost no background programs running), Windows 7, and Linux.
2. To separate personal data from the OS. My "MY Documents" folder is on a data partition, as my my iTunes folder and my mailstore folder. I can boot into any of my OSes and still have direct access to my mail, my bookmarks, my music, my videos, my personal data, and so forth.
3. To make taking backup images easier. I regularly use Ghost to make a disk image of my OSes, usually before installing something big or that I'm trying out. If I don't like the program, I can Ghost it back from one partition image (stored on the data partition) to the OS partition itself. People who say they "reinstall their OS every 6 months are totally nuts" as far as I'm concerned - they need a good partition imaging program and setup to easily roll back the OS after trying something.
4. The beauty of keeping the personal data off the OS partitions when I ghost one back, none of my data changes - it's all on the partition that doesn't get ghosted.
5. A lot of games can happily live outside the Program Files folder. I have a folder on my data drive called Steam Games and all the steam games live there. Even when that drive letter changes, all the exes in the Steam Games folder work directly by double-clicking the EXE. It's very slick.
-Llama