Using alt text on all of the images on your site is good practice for better SEO (search engine optimization).
When you're curious about something, what do you do?
You Google it.
Google does a bunch of voodoo magic and, no big deal, scans all of human knowledge pretty much instantly, and shows you results.
Having alt text on your images helps essentially helps people find you, your website, and your content and it's something you should do.
However, depending on what sort of content you have on your site, adding alt text can very well introduce some ugly problems.
If you use slide deck galleries, and you add alt text descriptions to all of the images on the images in your slide deck, you'll notice that the alt text will start showing up in the bottom corners of your slides! GROSS!
WIX has support articles about disabling or hiding this alt text, but it only offers the solution of using specific gallery widgets...which isn't really a good solution for people who want to use any gallery that they want for their site.
The best solution that I've found is to click your Slide Deck Gallery, or any other gallery that doesn't support hiding the alt text > Click Design > Click Customize Design > Click Text > Change BOTH font sizes to 0.
Voila, that simple. You have alt text for better SEO and it doesn't appear on your site.