Why is "#{String}" a common idiom in Ruby

Question

A Ruby dev I know asked this; my answer is below... Are there other, better reasons?

Why do so many Ruby programmers do

"#{string}"

rather than

string

since the second form is simpler and more efficient?

Answer 1

Is this a common idiom for Ruby developers? I don't see it that much.

Answer 2

Smaller changes when you later need to do more than simply get the value of the string, but also prepend/append to it at the point of use seems to be the best motivation I can find for that idiom.