Whether it is nobler for the conductor to sing while conducting or not . . . THAT is the question. And the answer is not simply yes or no. Here are some thoughts.
If a conductor can demonstrate a particular part, the direction of a phrase, the shape of a musical line, a special word needing attention . . . s/he will be further ahead. After all, a demonstration is worth a thousand words. It is literally how we all learned to speak! So do it . . . if you can. And do it, even if you can’t! (My choral mentor was famous for reverse psychology in this area. “If I can do it with my destroyed voice, you lot will sound magnificent!”)
The question is whether or not to sing while conducting. Well, an argument in favour would be that singing with your group is beneficial because it models the singing mode. They see you working it. And they are much more likely to mirror your intensity, your facial expression and your mouth/vowel shape than if you were at arm’s length, merely conducting.
In truth, I tend to sing with my groups when rehearsing . . . when I’m motivating and inspiring the song at the preparation level. In performance I have a whole set of other things to convey . . . which future TIPS will reveal.