It's best for safety to have it right at the point where is is neither too high, or low, but in a spot where you have perfect control of the piece you are jointing. Easier said than done, and I'd suggest starting low, and adding layers of 1/4" or 1/2" ply under the tool, and build it up till you hit that sweet spot, because until you actually get it there, it's all subjective.

That said, there is also something where if every tool in the shop was exactly the same height it gives you a bunch of similar height objects to use as support stations for longer work. Problem with that is a BS, and a drill press, versus a TS or jointer will be different heights to function well. So maybe 2 heights?