Leak cover under Distributor cap

When I recently replaced the rotor in my distributor I couldn`t get the leak cover to fit back in. The rotor I was given at the parts store was a slightly different shape than the old one and that made it impossible to replace the leak cover back.
I would have taken the rotor back, but I needed the car right then. I installed the new rotor without the leak cover and it ran great, so I didn`t sweat it.
Now, I`m starting to wonder. Do I really need this part? I`m assuming that it`s just an added protection against water/moisture, right?
Are there any other problems that I might face by not using this part :