Do you have enough memory to enable it and not have most of the memory used? If so then it really doesn't matter, its when your say using 105% or 110% of the memory in the compute clusters where it may help prevent things like swapping and ballooning which could be an issue, especially if you really restrict the memory in your vms. If you don't try and right size as much as possible, like giving a desktop more then 90% of what it's going to use, then that setting really isn't needed. Reservations only start really being a concern ones the host memory starts getting taxed a bit.
It is required if you using a hardware graphics card, but outside of that, there isn't a requirement to use it. In general, use that as a guideline, and test trying things that don't fit what your trying to do.
