I thought it might be nice to add one counter argument to this since I haven't seen anyone mention it previously. But aside from the toxic emote spam, emotes can be used strategically a couple of other ways:

To boost the morale of your team by using a well placed emote after an incredible play.

To inflict psychological damage on an opponent, effectively taunting them and goading them into focusing on you (this is great especially if youre playing a low priority job and you want to free up your AD carry to do more for your team).

These are just a few ways I use them and encourage others I mentor to use them. But there are other ways you can get creative. These are just a couple I havent seen mentioned.