[RobertKerans]

It doesn't really need studies per se because [specifically for web] justification doesn't work properly without significant overhead. You can easily justify badly (normally with a single property applied to the text), but to make that work well, the browser (or app, same is true there) will blindly split words and drastically adjust the tracking between words, leaving huge rivers in the text which unequivocally make things difficult to read. When setting text on the web, it's far more practical to set it ragged right, as it avoids this problem (with the trade-off that it may not be as pleasant to read as properly justified text).

In print, if I'm typesetting, I a. have a fixed container size within which to apply justification, b. have access to advanced justification settings that allow for smart word breaking based on word length, language and regex patterns, and c. on top of that as a final step I can work forwards through the text, manually breaking words or adjusting tracking on a per space basis to remove any remaining rivers.

On the web, this isn't available, so justification there is an extremely blunt and not particularly useful instrument