If your Mac is a year or two old, it's probably packed with 256GB of fast, flash-based memory. The problem grows more acute when you consider the growing popularity of solid-state drives. These files are living rent-free and taking space away from data you may actually want or need. Installing apps, and then uninstalling them, doesn't always get rid of all the associated libraries, temp files, app and browser caches, and logs that went along with the original app.
Whether you've been using your Mac for a few months or a few years, chances are that it's not giving you the performance and efficiency it could.
