Software engineers aren't special. Literally any job that requires a modicum of concentration, whether it's writing marketing copy or doing complex financial forecasts, means that interruptions are costly.
Of course there were "emergencies" and things so it was more like a team standard than a rule but it was phenomenal. When I got to my desk in the morning I always knew I'd have a solid block of time to get through the important work before I had to go to a bunch of meetings and take on more.