I agree it is good practice but there is a lack of consistency. Until retirement in 2009 I travelled frequently with a variety of airlines on long and short haul services. Some checked boarding passes at the aircraft, others did not.
Since retirement my flights have generally been domestic within Spain with infrequent trips to the UK either direct BIO-LHR or via CdG and that inconsistency still exists.
That said, my boarding pass always remains clutched in sweaty fingers until I am seated and thereafter in the seat pocket. Not difficult but more consistency would help.