Few lead sheets I use, whether they belong to the band, my own arrangements, or ones shared by others at a meet, have chord diagrams. The only time we've used them is when there's a chord or two that band members have not seen or learned.
Funnily enough, I need to sing to be able to play. In the cases where, for example, our MD greys out lyrics on an instrument breakout, I add the lyrics back so I can at least sing to myself; Then I can play the tune.
Different strokes for different folks I guess.