What is compromised by leaving Sprocket O-ring out?

[mikthebik]

Just replaced the rear tire on my F3S and noticed the infamous (sometimes missing) sprocket O-ring was pinched and distorted. Whatever sealing function it originally provided was severely compromised. I called for the part at the local dealer, but the wait was over a week. I decided to leave it out this time and order a couple of new ones (one as a spare) for the next tire change. I'm wondering what I may be compromising by leaving it out. The F3S is mainly my local trike and never gets ridden in rain. That honor will go to my "new" 2018 RTL. I just changed rear the tire on it, and the Oring is in good shape. If the Oring is meant as a last stand water seal, its omission shouldn't be a problem. Rear tire on each Spyder is now a General Altimax RT45.