An important point to remember about virtual memory (swap file space) is that if you let Windows manage it, the file size is dynamic. This means that Windows will grow and shrink the file as necessary and as the demands of the apps running and the OS change.

This leads to two problems. Firstly, the swap file can become fragmented (non-contiguous set of clusters allocated to the file), thereby slowing access to it. Imagine that Windows sets a dynamic swap file space of 1Gb based on usage requirements. Later your usage patterns change a bit and Windows decides to reduce it to say 750Mb (this can happen more often than you think). This leaves a chunk of 250Mb available to the file system. You then happen to install a large app or game, move some files around, extract some new archives, or whatever. These changes may then cause the 250Mb free space chunk to be used up. Then lets say you start up Poser/Bryce/3DS/Whatever and start a nice big project. Windows now realises that you do not have enough swap space any more so it increases the size to 1Gb again, or perhaps even more. Now there is a problem because the 250Mb of free space that follows on from the 750Mb of space the swap file occupies, is used up, so Windows allocates another 250Mb of space elsewhere on the drive to increase the swap file size. Instant swap file fragmentation! Now imagine this happening once a day for a month. Your swap file can end up split into many chunks.

Secondly, working with a file that changes in size is slower than working with a fixed file size and just populating the file with data or clearing parts of the file after use. If you manually set both the minimum and maximum swap file sizes to the same value this will created a static swap file of that size. This value should be the Recommended Size that Windows displays at the bottom of the window in My Computer/Properties/Advanced/Performance/Advanced/Virtual Memory.

There is a lot of supporting information on the 'net regarding these changes and their impact on performance. I would suggest reading up on the subject more before following anyone's advice.

As per usual, just my 2c.