I think that depends on how much propagation you plan on doing, Carol, but warm soil will definitely encourage germination. For a good collection of seed-starting tips, check out this article from Fine Gardening:
Douglas, Thanks for the link. It was very helpful.
You're welcome, Carol. Glad it helped.
My mat gets a workout every spring. Don't worry if it smells like hot rubber at first....the odor will diminish.
Walter, Do you start your seeds indoors?
yes....tomatoes and annual flowers usually
Just ordered my grow mat. Can't wait to get it...