A plugin is extra PHP on your site. The directory is full of tools. Most sites need a handful: spam, backups, SEO basics, a cache you understand.
Before install
What job? Is it in WordPress already? Last update? Reviews that mention breakage, not just stars.
After install
If you cannot explain it in one sentence, remove it. Two plugins that do the same job will fight.
Security
Delete unused plugins, not just deactivate. Keep PHP current. A forgotten builder is how old shortcodes survive in the database.
