I'm not sure I fully understand your question, but what you are describing is what photographers refer to as filters. I lot of photogs like to put a UV or Skylight or similar filter on their lenses with the belief that it will protect the big, expensive objective lens. This is actually one of the controversial subjects on photography sites where it comes up again and again.
The pros for that practice is that it's cheaper to replace a $40 filter compared to a kilobuck lens. It gets wet, it get dirty, no big deal, you can clean it easily.
The cons of that practice are multiple.
1- You're putting a cheap glass in front of your super-expensive lens. The counter is to buy the best filter you can, but the issue of artifacts remains.
2- If you break the filter, it will hit your objective lens and damage it
3- You can damage the filter housing a lot easier that the objective bell and break the glass or distort it so it doesn't come off.
4- Filters other than UV/Skylight will slow down your lens.
For example, the polarizer you have on the scope is probably equivalent to a full F-stop. Ok on super bright days, not so good other times.
Also, you must understand that filters are nowhere near as strong or solid and riflescope optics. They are not designed to be on riflescopes and can (and will) break after repeated firings. I have experimented with various color filters to see the effect of mirage perception, but I don't leave them on for long and I did pay good money for decent ones.
For protection from dust and rain and impacts, the best thing on a riflescope is the sunshade. Mine are on all the time.
And FYI, I long ago removed all skylight filters from my camera lenses. However, if I go into an environment where the likelihood of damage to the lenses due to environment factors, such as blowing sand, a welding shop or some such, I will put on a UV/Skylight filter for that eventuality, then take them off when done.