Have you ever hunted with a rifle and a scope? How is a lens any different? Have you ever hunted with glasses? How is a lens any different? There are a lot of good reasons to use a lens if it is legal in your state. Does it get some rain on it if it is raining, yes, but so do your glasses, if you wear glasses. Most of the time you don't hunt in the rain but if you did and it was a problem, take the lens out. That takes about 30 seconds or less. As for dirt, glare and frost, I've never had a problem with that. If for some reason I did, I would take a moment and clean it or clear it. As for benefits, for some, their eyes are not able to see distances clearly. A lens helps. For me, during low light, the lens brightens the available light. Also, at dawn and dusk, a lens can help identify at a distance if the incoming deer is worth preparing for long before he might spot you. For example, this past season, I had a deer at 75 yards eating acorns 20 minutes before dusk. I held the bow up, without drawing, and got a look at his rack long before he got close. This is just a few a many reasons a lens comes in handy.