Agreed, for most real world softwares, the cost of GC is irrelevant. But there are still some programs like databases or game engines where the cost can start adding up. That's when you measure and optimize.

What does GC cost? For Caddy with an incredibly synthetic http only benchmark it costs about 2ms of latency and somewhat less throughput. Worth it in an incredibly artificial benchmark? Perhaps. However when it comes to real world usage the cost is a significantly smaller piece of the pie.