Every extra second of load time costs conversions, and the cost compounds on mobile networks. Speed is not a nice-to-have that engineers can fit in later; it is a product requirement.

The wins are rarely exotic. Ship less JavaScript, size images properly, cache aggressively at the edge and measure real users rather than lab scores.

Set a performance budget at the start of a project and treat a breach like a failing test. Teams that do this stay fast for years; teams that do not spend a quarter on a rescue project.