Google's John Mueller made it loud and clear on Twitter that you should try to use anchor text in your links and alt text in your images. He said "I wouldn't leave it out if you can avoid it" when he was talking about anchor text in your links and alt text in your images.
Here are the tweets:
@abondance_com @methode Yes, but anchor text (and image alt text) helps us quite a bit in understanding context, so I wouldn't leave it out if you can avoid it.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) May 15, 2017
This is probably obvious to many SEOs but truth is, many many webmasters and writers don't bother doing these things, including myself many times. Just too busy trying to push out content for the majority of our readers than add those details.
But yes, it is helpful and useful and should be added when possible.
Forum discussion at Twitter.