When do you start thinking about a load balancer?

Hey everyone, I've been thinking about how to scale our systems. We're growing pretty consistently, and it's got me wondering when we should introduce a load balancer. I'm not sure if it's just about how much traffic we get, or if things like how complicated our apps are, or if we absolutely need them to be available all the time, play a part too. I'm really interested to hear when you guys decided to add one, and what made you pull the trigger.