No danger. If it is too large, it may slow your system a little from the increased reading/writing to the drive while the system is using it. I have found that allowing the system to manage its size gives better overall performance.
If you have 2-4GBs of RAM, make it the same size as your RAM. If you have more RAM than that , I wouldn't set it at more than 4GB.
There used to be great debate about this. If you are using Win7 let the os manage the VM. Most systems today have so much RAM that the VM comes into less use. However windows and sum programs require it to run properly so we can not eliminate it 100%.