Also if you have moderately long lived requests, if one server starts to get overloaded and it starts to slow down, new requests will still be sent to that serv

Also if you have moderately long lived requests, if one server starts to get overloaded and it starts to slow down, new requests will still be sent to that server, which will make it more overloaded and slower, and jobs start to build up on that server, making it slower and slower.