Mechanics wire is different than safety wire, mechanics wire is soft, safety wire harder and doesn't really stretch.
I use mechanics wire to hold things in place.(like prepping my exhaust, measuring for brackets, bend, etc), and is quite reusable later on.
I'd never use mechanics wire to use as safety wire through bolts/nuts to secure them, it's not what it for, nor would I use safety wire to tie up an exhaust to measure things out, kind of a waste.
But that's just me, but do know they are two different things for two different purposes.