More often than not you either didn't finish the service or continued serving past initial descent in violation of company policy in order to finish up. If the flight was on a 717 i'd say sure but a 757 has 179 economy seats (including comfort+). A 1 hour flight has about 25 minutes of useful serving time. That's 10-12 minutes to get the double ding and get the carts set up and up the aisle and then stopping service at the top of descent which is 25 minutes out. So 3 flight attendants have to serve 179 passengers in 25 minutes. That's 60 passengers per flight attendant, or 1 every 22-25 seconds without any interruption. If there was no pouring and you could just hand out a small can to everyone then it would save some time but they don't want us doing that.