Screech helps you beat Starmie sometimes, I believe Screech'd Hyper Beam is an OHKO. However, Body Slam helps you paralyze things and does more damage when it crits than Slash does.
When I built a team around Zapdos, I made sure everyone except Zapdos was able to touch Golem and Rhydon so they'd be sacrificed for something better sometime. That means Surf on Snorlax and Mega Drain on Exeggutor and Gengar. Not saying you should use this, but especially the Surfing Snorlax brought many of them down.