Like the title says, I'd like to know the difference in nuance and usage between 「することはない」 and 「しなくてもいい」。
「謝らなくてもいいよ」 vs. 「謝ることはないよ」
To me, they both sound like "You don't have to apologize [for that]." On one hand, 「…なくてもいい」 sounds slightly more conversational, but I think I've heard 「…ことはない」 in conversation too.
Also, in this answer, it says that 「…ことはない」 might have the nuance of something you don't have to do and probably shouldn't do. So maybe 「…なくてもいい」 means that you don't have to do it, but it's fine if you do.
Can anyone provide some insights into differences between these two grammar points?