Also, there seems to be A/B testing w.r.t email id requirement when signing up on web i.e. it's not optional all the time. Doesn't seem to be the case with mob

Also, there seems to be A/B testing w.r.t email id requirement when signing up on web i.e. it's not optional all the time. Doesn't seem to be the case with mobile app, last time I checked. Seems like another way to push App adoption.