When to mount?

I still don't consider myself a pro, but I have recently sold a couple of framed prints. Both were 12x18 and I had them mounted on 50pt. board. I have prints of my own that are this size without mounting board, and I've noticed that they do wrinkle, so I had these mounted.

It does add to the cost of production so my question is what is the minimum size print that you mount? Is there a point where mounting is, well, pointless?

I don't mount, rather use linen tape to hold to board,I always use a backer board, so you see a single board behind the picture. Never worked smaller than 8x10 for mounting to date.

Usually I don't vacuum mount my prints, not very archival (for methods I can do at home)

I recommend to my clients anything above 11x14 they mount. Of course I will mount size they wish

Thank you for the responses. I figured I should mount prints 12x18 or larger, but wasn't sure about doing prints smaller than this (say 8x10 or 8x12).