Not exactly the same. There are a few reason I might mute someone (opposed to unfollow):

1) They don't know I've muted them, which can be nice for personal friends that are just too damn chatty.

2) They can still DM me, again useful for closer acquaintances.

3) I'll often mute temporarily, e.g., I'll probably mute several people for a week during the RNC convention, because they'll be much chattier than usual. Or I just recently muted somebody who would not stop with Brexit articles. I care about it, but as a USA citizen, I don't need 70 tweets a day about it.

4) I still see replies to the muted person (from other people I follow). I don't see tweets directed to other people unless I also follow them. So if muted-friend-1 tweets something and unmuted-friend-2 responds to 1, I'll see that tweet and can swipe over to see the full conversation. IOW, I still see "@mutedfriend that's awesome!", whereas if I unfollowed, I would only see responses that purposefully broaden their reach, e.g., ".@mutedfriend blah".

Anyway, not a huge difference, but yes, there are enough small differences that I'll often choose to mute rather than delete/unfollow.

You can mute someone's retweets, while still seeing all tweets directly posted by that person. That's what I was referring to above.

But it can also be useful to just outright temporarily mute someone who's at an event or something and swamping your timeline with irrelevant tweets that you know are timeboxed and will soon return to normal. A 7 day mute or whatever beats unfollowing and forgetting to refollow.