As pp mentioned use the mat after you've already put the fondant on.
The only reason I can see that you would want to put it on first is if you were using a roller with a pattern on it. Like this one:
http://www.wilton.com/store/site/product.cfm?id=109A9114-423B-522D-F10BD5197BC1A327&killnav=1
I've never used one of these so am not sure how to best go about it.
Oh I see!
I was thinking as you roll out the fondant you roll it onto the mat and then put it on the cake. I have to make mini cakes for a party and thought that would make it look fancy and be easier. So even on those, I put the impressions on the cakes with the fondant?
Thanks
Quote by @%username% on %date%
%body%