There 2 things i can think of:
-Prerequisites installations, UE4 attempts to install required dependencies, most impotently proper c++ runtime (but there high chance you already have that)
-File type association settings, most impotently for *.uproject files), so when you double click it open UE4 of proper version + add right click options for project UE4 version switching and VS file generation
UE4 dont do any visual changes to your computer, if anything it only has to do with UE4 proper operation