But a matte can help in preservation of prints, and especially original artwork. The matte will keep the print pulled back from the glass, so you will not have any fear of transfer of ink from the paper print to the glass, especially in higher humidity areas. If you don't use a matte, there are spacers which can be used in the better frames which stay between the glass and the print at the far edges behind the framed edge.
I'm guilty myself though. I don't take the precautions with my small collection of lithos. Original art, sure. None of that touches glass, all gets the custom treatment, and extra UV protection glass too. But the poor lithos just get thrown into a pre-made Michael's frame with 'el cheapo glass...
Just some thoughts.