With medium format folders, you tend to frame a bit loose and then crop later. A big issue with most folders is parallax.
Most older folding cameras don't have framelines and certainly don't have parallax marks, so you must remember to make your own adjustment.
For tight portraits, a folder probably isn't the best tool. I think they're fine for environmental portraits as Frank stated.
Here's one that I snapped quickly, using a Zeiss Ikon Super Ikonta 532/16 (with the coated Tessar). This is a front-cell focusing lens, by the way. This was Agfapan APX 100: