I guess the answer is "it depends".

I have two on mine and use them both. But I have my bench set up for the two.

As you can see, I use an old leg vice on the front but it could be a regular vice too. I have a sliding deadman on the front to support the end of longer boards. As it's name implies it slides in a dado and the support is held in place by a couple of dowel pins. So I could put a wide board up there if I need.

My table has dog holes in it that line up with the end vice. I attached a large block with a dog hole to the vice. I can clamp boards flat on the bench to work on. After using this bench for a few months now I love it and can't imagine not having a proper bench to work on.
If I were to build another I would build it with the two vices setup like this one. I find them extremely useful and use both of them all the time. But you may work different them me and this might not suit your work style.