Spotlight is great for so many things. Launching apps. If I know a filename, I can just type a couple of words from the name and pull it up without going into Finder. It will do a website search. Unit conversions, as you say (including currency conversions). Math operations. Find contacts or calendar events. Weather. Timezones. Driving directions. Apparently you can pull up sports scores or stock tickers, though I've never had a reason to do either of those. It's brilliant.