I have used full glass canopies on every tanks I have ever had. I have still had jumpers - flame hawk and a neon dottyback, in my old tank - there were square cutouts around pipes. I still can't say for certain how my McCoskers Wrasse got out of my current tank. I have foam around the return pipes. All I can figure is the foam must have gotten squished when I removed the lid during a water change.
That said the wrasse did regularly hit the glass canopy. Loudly. He also jumped out at least 3 times when I had the lid open to put in food. He had a death wish.
If you use mesh, make sure the opennings are visibly smaller than the smallest diameter fish.
As for gas/heat exchange, you sump and skimmer take care of gas exchange. Since my lights (LED) hang above the tank, not in a closed canopy, the glass helps to keep heat and humidity in, which I consider a plus.
The glass also keep dust, dog hair, etc out.