Back in the 'before times' (before COVID-19 forced many of us to work from home), we often had a work computer and a home computer. While you could - if you had time and knew where to look - hunt down all your own leftover files and clean them, your Mac doesn't have a built-in way to find and remove this waste. New updates, uninstalls, extra translations, and ongoing usage create digital detritus that takes up precious storage space while bogging down performance.
Even if we're super-fastidious, our computers generate their own junk.
