I think there are two major concerns with mounting any press -
1) The tremendous leverage, that others have mentioned, imparted into the bench when you operate the ram
2) The height of the press/ram handle/shell plate as you operate the thing, either standing or sitting
I'll only address the second one, the HEIGHT concern...
When operating the press, you want to be able, obviously, to comfortably (EFFICIENTLY) cycle the press handle from top to bottom. Most presses involve a pretty long "throw". And it takes not only a reasonable amount of force, but the ability to "feel" the die moving over the case, primer seating etc. And most critical is that you will do that movement a bazillion times.
I suggest, place your new press on stacked cardboard boxes, milk crates, ammo cans, anything, to experiment with height settings. Set it at some height and then cycle the ram arm. You'll need someone else to help hold the press in place while you do that. But one way or another, IMAGINE making that arm and body movement over and over again while you're sitting or standing, whichever you prefer. Stick a little slab of plywood under your stack of boxes and see what it's like 3/4 inches higher. Take something out of the stack and see what it's like lower etc. Find the spot where you think it's ideal for your body movement to be most efficient in cycling that one armed bandit.
The other height concern is being able to SEE into the case that's been charged with powder, prior to seating a bullet. Moving your press up or down an inch or two will vary your ability to see that powder charge. You MUST be able to verify the powder in the case visually. A good press height will allow you to do that in a fraction of a second. A poor press height will force you to move your body a lot to get to a spot where you can see the powder.
Here's my pics from another thread. Stacked slabs of 3/4 plywood make up the riser for my press. I can remove or add slabs if I want to make the press sit higher or lower -
I personally prefer to stand while operating the press. The ram handle is much easier to operate using my entire upper body than it is using just my one arm movement (like a slot machine). But everyone is different. Stand, sit, whatever you do, it's important to find an ergonomically efficient way to make it happen. Because you'll be making it happen over and over and over again.
Sgt Lumpy