I've finished the Holy Family picture I've been working on for the past 2 1/2 yrs. (before I found this wonderful site)! It's wonderful to have it finished so I can start on 1 of the SQ patterns that have been patiently waiting in my closet for their turn. I plan to take it to Michael's (during the next 50% sale) for conservation mounting (no adhesives to break down fabric/fibers) and they have spacers which can leave room for stitches not to get crushed. So my question is does the mat serve any purpose or is it strictly a preference thing? Even when you look at paintings, some have a mat & some don't so I'm not sure.
If you have the spacer, then the mat is purely an aesthetic device. But if you have a mat, then you do not necessarily need any additional spacer. I have framed several things with no mat, but have a spacer (of varying thickness, depending on if the piece has embellishments - beads - or not):
http://tinyurl.com/cdt2nq - this piece has a spacer that is 1/8" tall, as this has size 8/0 beads, and a big ss spider charm attached.
http://tinyurl.com/c9ums4 , http://tinyurl.com/czehzq , and http://tinyurl.com/df3c5p all are framed without mats, and have a 1/16" spacer between the glass & the work, as they are all just stitched, no embellishments. There's a thinner spacer material available, which I would have used if I'd had any...
This piece http://tinyurl.com/dysk29 is framed with mat, no additional spacer.
So long as you have one or the other at a minimum, it's up to you whether or not to mat a piece - and take into account the added expense in the materials to accommodate a mat. That last one I linked, the one with the mat, is a Quaker piece, and traditionally, Quakers don't have mats, the frame goes right to the edge of the stitching - but as I did that over-1 on 32ct, it would have been pretty small without the mat - and I'm not really much of a traditionalist anyway
And of course, this isi all dependent on having glass in the frame - a LOT of people do not put glass in the frame, but as I live with animals and a smoker, glass is a must.