Just as a couple examples, this was taken from the front during the toast, at 170mm and cropped. To get a decent shot with a 35 I'd have had to be way too close to them, and would be rather disruptive.
This dance with the father of the bride was at 155mm:
I probably could have gotten closer, but especially as I was not the pro for the wedding I didn't want to be on the dance floor. But neither was the pro, they were a bit closer not not much.
On the other hand, a bit later I wanted to be really wide. This was 19mm:
I just can't imagine doing candids, or chapel scenes, with only a 35mm. Would you really?