The last hit on the beast is the only hit that counts so they can be easily stolen by the other team. If all players on both teams are off respawn and you go after a beast then you are leaving your team in a 4v5 on the rest of the map. Against any half decent team you'll either lose the team fight mid or have home decapped. This is why it's not worth going after beasts unless the opposing team has players on respawn, your team has no one on respawn, you have both home and mid and you can dps the beast down before the enemy respawns. Beasts can be used to get a clutch victory especially if your down 475 to 490 and you can burst the beast down before the other team ticks to 500. Decap far, steal beast from other team, kill player that was trying to kill beast, gg.