Why mobile performance matters more than it looks

Every audit we run turns up some version of this. Mobile performance is easy to treat as a detail, and that is exactly why it is worth a few minutes of attention.

Real-world numbers from actual visitors matter more than a score produced on a fast laptop. Write the reasoning down alongside the decision, because the reasoning is what changes first.

Why it matters

Phones have less processing power and worse networks. Where this goes wrong is almost never a lack of knowledge. Doing this properly once is usually cheaper than doing it approximately three times.

Test on mid-range devices, not just the newest. Where this goes wrong is almost never a lack of knowledge. It is worth deciding this deliberately rather than inheriting whatever the last person set up.

Where it usually goes wrong

JavaScript costs far more on mobile than on desktop. Where this goes wrong is almost never a lack of knowledge. Assume whoever inherits this will have half your context and none of your patience.

How to tell if yours is fine

Performance work is mostly subtraction, which makes it unpopular and effective. Three things worth confirming about mobile performance before you move on:

• Someone can say what the current setup is without going to look
• Phones have less processing power and worse networks — and you know whether that is true here
• There is a way to tell whether the last change to this helped

Most of the value here comes from doing the first two things, not all of them.