even when two (or more) words are largely synonymous, often one of them will convey precisely what you mean, while another one will mostly do just as well, except for exactly those contexts in which the difference is significant. i assure you, sometimes it matters rather a lot whether the safety of sth. or so. is ensured or insured, so it's smart to make sure we're able to make the distinction. sure, i'm splitting a hair four ways here, but once you start sliding down that slippery slope, you might as well declare 'affect' and 'effect' synonymous, and then you'd say 'literally' is interchangeable with 'figuratively', and in the end you'll use only one word for everything, and that word will be 'fuck', and your parents will stop talking with you and cut you out of their will.