I have been using Better Twitch TV for years and here are my reasons.
Custom emotes – You can use custom emotes for your channel and they can even be animated. You can even display other Twitch Better TV emotes in your or other streamers chat by switching them on.
Host button – You can add an easy to use host button to all streams you follow, which makes it easier to stream.
Discord sync – You can synchronize your emotes with Discord. Allowing them to be used by anyone in any Discord.
Emote menu – This menu will add tons of Better Twitch TV emotes for use in chat.
Hide Prime promotions – You can turn these off if they annoy you.
Hide recommended channels – Another way to reduce your annoyance.
Hide Twitch extensions – If you would rather not have pesky extensions showing up on your screen, block them.
Left side chat (my favorite) – Put chat on the left side of the screen.
Show deleted messages – View deleted messages even if they are removed by a bot.