The only pre-cut mats I currently use are these little 8x10 mats. They have a generically-sized cutout area that can be used either horizontally or vertically. It follows that most of my prints are therefore cropped somewhat. I try to compensate for this by signing both the mat (in pencil) and the photo (in archival ink). If someone wants to take out the photo down the road they'll have an uncropped, signed print.
That's the theory, anyway. In practice, these 8x10 frames, of which I have around 20 for sale in my booth for $30.00 each, don't really sell at all. I think that they're perceived as being too small.
Photo: 2005 Redwood Pix in 8x10 Format Frame with Pre-Cut Mat—Marin County, 2010