Think of a file system as a book. There is a table of contents, and then all the files are in the subsequent pages. Deleting a file is typically done by removing the entry in the table of contents, the pages are untouched, which means its a very minimal change.

Deleting an app should be fine, but if its an older phone, you may want to look for a migration path, as hardware will fail as it ages. Could be anything, battery, charging ports, buttons. One day it will die.