Well. To put it simply, it resets your game to a known state.
If you look at the game as 3 pieces you will see why.
- The application itself. This is often not the problem, but it can at times be the wrong version or get screwed up from changes in the game. This gets reset to an exact state on reinstall.
- Game update files. Whenever you see it say downloading files 10/100 or whatever it’s basucally sucking down files that contain differences between the application build itself and the current game. This can be anything as minor as chest drops to anything as major as changing towers or dragons. - these are semi prone to being corrupt and can also receive accidental changes and such. A reinstall forces these yonall get downloaded again
- Game data/cache. Information about your current progress in the game such as Your level you items your towers your dragons. The whole thing. They are all stored in a temporary cache. This cache is synchronized to the server in a way where the data in the server is validated, and should your cache get corrupted or something unallowed happen, more than likely a fresh copy of what’s on the server (database) will be a working copy.
When you reinstall it deletes everything. On android you can sometimes fix a lot of problems by just clearing your cache. (Of which I think technically contains both 2 and 3)
So it resets as much to a known state as is possible.
It is possible to have issue with the data on your account (needs support to fix) or your account to device association. Neither of which would be resolved by reinstalling.