I use Alfred to switch between applications using keyboard shortcuts. On average, I use Alfred 127 times per day, mostly to use keyboard shortcuts.
I recorded a three key shortcut and found it takes just under 0.4 seconds to complete. Changing between programs using a mouse takes about 1.5 second (though I would argue the variance is much higher if you need to dig around the screen or screens to find the window). As a Fermi estimate, I save 16 minutes per week and ~14 hours per year.
That’s just for switching between applications! I use keyboard shortcuts everywhere, especially when writing and editing text (90% of my work).