Page speed is one of the few levers that acts on both sides of the equation: it lowers what you pay for a click and raises what proportion of those clicks become leads.
The Two Mechanisms
Search platforms fold landing page experience into ad rank, so a slow page can cost more per click for the same position. On the other side, every additional second of load time costs visitors before they ever see your offer. You pay the higher price and receive fewer outcomes from it.
Measure the Right Page
Site-wide averages hide the problem. Look at the pages that carry paid traffic: campaign landing pages, product detail pages and the checkout or form flow. A fast blog with a slow checkout is still losing money on every campaign.
The Usual Causes
Unoptimised hero images, third-party scripts loaded before content, chat widgets and tracking tags stacked without a plan, and fonts requested from servers on the other side of the world. Most sites can remove a third of their script weight without losing a single measurement that matters.
What Good Looks Like
For a paid landing page, aim for a largest contentful paint under 2.5 seconds on a mid-range phone over a mobile connection, and keep total blocking time low enough that the form responds immediately. Test the page on a real device on a real network, not on a desktop with a fast connection.
Sequence
Fix speed before scaling spend. Every week of delay means paying the slow-page tax on traffic you were going to buy anyway, and rebuilding the campaign data you will need to judge whether the channel works.