If this is about OS buffers/cache it is absolute nonsense. In fact it will not improve but hurt performance. Whatever is in the OS' buffers (the biggest of them being the file cache) is there because it is needed often. The system "learns" which data is needed more often and which is needed only rarely. Rebooting destroys this (meta-)information and the learning process starts from point zero.

I have a suspicion about how this came: someone noticed that after rebooting the system the "fre" counter in vmstat is higher than in a long-running system. So there must be more free memory, right? No! When a system starts up it loads all the programs and then (i presume the system being well tuned) some memory is left over, which would be dedicated mainly to the disk cache. But as the system doesn't know what to cache it simply makes no sense to fill up this memory with anything. This is why "fre" is so high: the memory is not "free", but "unused". Once the system starts to process data, it dedicates the unused memory to caching these. Things oftenly needed will stay in the cache while things needed only once will get thrown out eventually, as other data are loaded. This way, as a "usage pattern" develops, the cache becomes more and more effective, because it holds the things most oftenly needed. This is what i meant with "the system learning" above. A reboot destroys this and starts this "learning" process anew.

By the way: it is really easy to make the "fre" memory counter go up: (mis-)tune the maxperm and minperm to really idiotic values so that the filecache is very small even if there is lots of memory available. Performance wil suffer greatly, but the "fre" counter will go up.

By and large a reboot is only needed for one purpose in a Unix system: to load a new kernel image! If you didn't change anything on your kernel you DO NOT HAVE TO REBOOT! Sometimes a reboot is used by sysadmins to bring the system back into a defined state ("reboot .... is good", as a proverbial bad rhyme goes). Whatever might have run on the system, now it is either gone or we can watch it as it develops. But to "reboot to improve performance" is absolute nonsense, in fact it will rather hurt performance.

I hope this helps.

bakunin