When automatic resolution is available there really is no reason not to use it. The auto computation is a fairly complex algorithm that factors in various vorpX/game settings that may impact the best possible aspect ratio/resolution. Disabling it will often result in less optimal performance.
Even more important are other automatic settings changes, which whenever available for a game typically make sure you get a perfectly matching FOV and/or less graphical glitches. Often these even include things required to get games working at all like choosing the right graphics API or a working AA mode.
You are of course free to dismiss all of that, but please don’t recommend doing so to newcomers. In the best case that makes things harder for no good reason, in the worst case it makes games unplayable with vorpX for average users entirely.