I am not a Windows expert, and I am telling this purely as a longtime user-of-Windows' perspective.
If you enable virtual memory:
- A large file (usually 1.5 times of physical memory size) is created at the root directory of the system (usually, c) drive. This file cannot be moved to another drive. If your system drive is a small SSD, and say you have a 16GB memory, this will really bother you.
- If you minimise a program and restore it after a long time (like several hours later), Windows will read the drive a lot, and the program becomes unresponsive for a while. Possibly, Windows had put all the memory of the program into the virtual memory and tries to restore the memory when activated.
- Real memory saved from 1 and 2 above may be utilised for file caching. File that was once read can be read super fast from the next time. Notice that, Windows does this whether virtual memory is used or not. It is just there would be more real RAM for this, if virtual memory is enabled. You may or may not notice the effect anyway.
If you disable virtual memory:
- You will not experience the first two annoyances in the "enable" section.
- If your RAM usage nears the size of the physical memory, yes "nears" not equals, Windows will constantly show a pop up message saying the system is running out of memory. For example, if you have 1GB of physical RAM and the Task Manager shows about 0.5GB of RAM is used, but Windows may keep showing the warning pop up.
- If your RAM usage really really nears the physical memory size, the entire system may become really really slow and unresponsive. Applications may crash without apparent reasons.
Other than that, I have not experienced any downside of disabling virtual memory. I think virtual memory technology was invented long time ago when PCs have 8MB or 16MB of RAM (MB not GB). When I was a college student I took an Operating Systems class, and learnt how virtual memory worked. It was a general mechanism, not Windows-specific, though. It may have been useful when PCs had really small amount of RAM, but now anyone can easily afford 16GB on one's desktop. I think virtual memory is not so useful anymore, unless you are using a laptop which has unexpandable 4GB RAM. I personally have disabled it on my PC which has 16GB of RAM.
In your case, if you are 100% sure that your RAM usage will never exceed 5GB (since you have 6GB), go ahead and disable it.