Print size depends on a lot of things, not the least of which is subject matter. The majority of my images work best at large sizes but some are better if kept small. Several years ago I started printing large (24”x30” and 24”x36”) prints and they continue to be very popular. I think part of the reason is the WOW factor but beyond that, a 24x30 matted and framed to 34x40 is large enough to command a space above a sofa or credenza where it might take several smaller images in a grouping to accomplish the same thing. Because of that, I have sold a lot of work for use in offices or commercial buildings where smaller pieces just don’t have enough impact.
My negatives are all 4x5 or 5x7 so the grain/sharpness factor is seldom an issue. My darkroom can handle up to 20x24 in trays and about 20 years ago I built my first developing tube for larger prints from plastic sewer pipe. I still use it but I have since acquired a Kodak tube that does up to 30x40.
I do sell a lot of 8x10’s (that is about as small as I go) but I hate making them. My first print from a new negative is usually a 16x20. I feel that at that size I can judge the tonal scale etc. better than on a smaller print.