Not using labels when using icons is an extremely bad idea. Here is an (dated) article that points out the issues:
https://www.nngroup.com/articles/icon-usability/
Unless it is something that is instantly recognizable (attachment icon, editor icons) it is never a good idea to remove the label.
If it is being done from a stand point of needing more space for the navigation, look at using Bolt by
@Russ /
@Pixel Exit as he probably has the better side navigation system currently. I can provide you the CSS (Maybe template mods, can't remember) changes I made to make the navigation collapse to icon, rather than hiding completely. The difference when removing label with this is that the default is to show the label, and people can choose if they want to collapse or not (I normally do, but I also use my site 24/7).
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