“Avoid premature optimization” is a popular and effective mantra. It’s a defense against the temptation to worry about speed and performance before you even have a working feature. Sadly, this often ends up interpreted as “forget about optimization”, and that’s a big honking mistake.
Speed matters. The magic number has changed over time, but the basic rule hasn’t: the longer a page takes to load, the less likely people are to use it.
Too often programmers quote The Mantra and then neglect to ever optimize. The idea is to avoid focusing on speed too soon, but not forever.
The best way to avoid forgetting about performance is to make it a feature. When building your backlog, pop in a story that goes like this:
That way, everyone understands the value of speed, and it doesn’t get sacrificed for more easily visible features.