This fire has been stoked many times here. However, speaking as a kind of Tenor, the 8 is not a redundant marking, and I might conceivably think the part is at Treble pitch in the absence of other indications, particularly in Early Music.
As a notator, the real problem comes if you want to switch clefs: you cannot accurately switch to another clef in the Tenor voice instrument; nor use the G8 clef in any other voice. It’s possible that a generic “Men’s” part might switch between F and G8 clefs.
As an editor, I often transcribe music in C4 clef, which I then change to a modern Tenor part. I also produce editions in different transpositions, where an Alto part in one key may be a Tenor part in another.
For those that want it, there’s a solution here in the form of a ‘real’ working G8 clef.