Why does reinstalling an app sometimes work to fix problems? It's not uncommon for people to recommend reinstalling an Android app if it isn't working properly.  For example, see this post on this site.

Why does this sometimes work?  What is goes wrong with the Android app installation that allows them to load and partially work, but not fully work as expected?
It's not necessarily the installation process which goes wrong.

A file which is non-essential (a sound file for example) may have been corrupted for any number of reasons, and a simple re-install re-writes the corrupted file.

It's the same principle as with a computer application. An error pops up at a random time, yet the rest of the program still works.