This should be done after rebooting, but before letting the machine sleep.
After you restart, run a normal session of use -- using the machine and programs like you normally do.
Go to Terminal and type in vm_stat
Look at pageouts... is it a big number?
Unless you have a high pageout number, you're most likely not resorting to having to use the VM Manager to much -- aka, you have enough memory so don't worry.
If it's a high number, you are probably thin on memory.
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Page swaps are energy consuming on a portable, though it should swap the memory to the HD to power the machine down into deep sleep...
So letting depending on how many times you let the machine sleep, the pageout numbers will be huge -- until you restart the machine.
EDIT: Page swaps aren't eating up memory, but letting you use more virtual memory than you have physical memory.
Before in OS 9, we'd be getting a lot of "out of memory" errors as the memory space becomes fragmented or we run out of memory.
OS X manages memory for us much better so we don't have to worry, just makes things slow at times.
