If you are talking about NYC firms they are brutal and mercenary. On late Friday afternoons a new assignment from a partner would end up in your inbox. With a Monday due date. So you have to work all weekend.
Or, in other departments, on early Friday evenings, the partner in charge of the associates committee would be prowling the hallways looking for associates to receive new assignments. Just to make sure the junior associates had something to keep them busy over the weekend. I was a mid-level in a smaller practice group so I would usually get my weekend assignment directly from my senior partner delivered by a messenger.
I remember, just after I moved to NY, I wanted to go to a Pitt game in Pittsburgh. I left LaGuardia Saturday morning, flew to the game, flew back that night and was working in the office 'til after midnight.
Not much fun.