It's the little things that add up. At work, or when you're on the computer at home, those little things include clicking from one window to another window, over and over.
Say you're writing an email about last month's expenses. Normally, you'd have your email open as you're typing. But, you need to see your budget, perhaps on an Excel spreadsheet, so you click over to that to check the figures.
You end up wasting a lot of time switching from email to Excel, then back to email, then back to Excel. That type of wasted time occurs a lot, no matter which programs you're using.
Just think about the last time you were posting photos to Facebook. You have Facebook open, but you also have your camera roll minimized to your taskbar. You keep clicking from one to the other. But you don't need to waste time with a simple program.