5 Reasons not to use Wix to build a website
1. Accessibility issues: with Wix, many features like image galleries, fancy navigation menus are rendered using some obfuscated javascript techniques, it means these kinds of content won't render in a browser that has no javascript engine (mostly 'command line interface' browsers) or it's disabled by a user (for privacy, speed, or other reasons).
2. It's very resource intensive in general, but in particular the administrative area. The backend is so heavily loaded with javasript code that with an inexpensive 2.1GHz Celeron computer equipped with 4GB of RAM I barely managed to view and download some photos uploaded to the system, editing pages was so glitchy that I'd say in any practical terms it was near impossible.
Though, using the same computer I was able to browse and edit WordPress and Joomla powered websites normally.
On some really simple Wix powered websites I've checked, pages contained the CSS code with enormous amount of web font declarations to load. One of these CSS fragments I studed weighted about 270 kilobytes alone, referencing roughly speaking 600 fonts! Though some other Wix powered websited had kind of acceptable number of font declarations (about 17). Why some their websites have 600 and others 17 web font declarations I have no idea.
For comparison, when I build a simple and slick template the amount of all the CSS code included is usually around 20 to 50 kilobytes.
Once I visited a simple Wix powered brochure website using an older computer with 1GB of RAM. The pages contained only text and some regular sized images here and there. I was stunned by how glitchy the browsing experience was, when clicking a link to the next page there was a few seconds delay and freezing. Browsing similar websites powered by WordPress, Joomla, or written in plain HTML I didn't have those issues.
3. Yet another, rather important reason to stay away from Wix, is that the pages it generates do not adjust to accomodate a smaller screen on mobile devices. I've heard they say they are mobile friendly, but I've never seen a responsive web design on Wix powered websites I worked with.
4. It is difficult to migrate from Wix. The system has no "export" functionality and when you'll want to move your site to another platform, you'll to spend a lot of time manually selecting, copying, and pasting your writings, saving images one by one through the administrative area, or hiring someone to do this very time consuming job for you.
Once I had to migrate a Wix website to WordPress, I was surprised to see that I could not even save images from galleries in a normal way via the front end, when I checked the src attribute of the images through the web console, it pointed to a different picture that contained only partial graphic of the one displayed.
5. Page loading speeds are rather slow, it's especially noticeable with slower or/and less stable internet connection, and it comes from the reason 2, as even the simplest web page will need to load a bunch of scripts, CSS and font files.
Conclusion
It may be easy and quick to start publishing with Wix for a beginner, but once you gain some knowlege on how a real world website should run, you'll probably see Wix more like a toy.