Some do, but most plays don’t require a second throw to get an out.
Good communication, a good understanding of the situation and a strong arm often will get you where you need to go.
However, planning and practicing for all possibilities is the work of a great player and team.
And more importantly, that strong play won’t be perfect every time and you’ll be glad that relay player was at the ready.
Expect the best, plan for the worst. Or something like that.