I would always be wary of any kind of damage to glass on a aquarium. The size of the crack, size of the aquarium, location of the crack, type of crack, and many other factors can play a roll. That said, yours doesn't look THAT bad. Is it chipped or is there cracking that can spread? It doesn't look like it's even close to the silicon so that is good. I had a nice chip in my 90g oceanic. Those are made with thick glass as well. Threw some epoxy on there and all was well for 3+ years before I sold it.