why is my mac so slow

When you start using Mac optimization software, essentially you're allowing a knowledgeable developer to access your computer and run maintenance scripts and low-level commands on it. The result should be a much cleaner, better performing Mac computer, since these commands remove the system, user, third party and Apple-made app cache files from your Mac to reclaim the disk space occupied by these temporary files. A cache is like trashcan, if no one takes it out, it will keep on building up until it becomes too much for the home (or, in this case, the system) to tolerate. These Mac cleaning tools also include useful utilities such as memory cleaning and a duplicate finder, as well as allowing you to control your privacy.

Your Mac includes daily, weekly and monthly scripts to serve this purpose, so macOS scans your computer and removes some old caches, log files and the like, but sometimes this just isn't enough. This is where third party Mac cleanup programs come in handy, but you can do it just as well yourself if you have enough knowledge about how mac OS works, what kind of low-level commands you need to run in Terminal and which files you can safely remove from the system library without harming the performance of your Mac why is my mac so slow