How duplicated preloader may affect your site?

What is Preloader, Instant Page loader?

When people on your site browsing on the store, hovering links on desktop and mobile, people expect the next page they go to will load as fast as it can. So, make sure that the loading time of a page is fast may give an edge.

Amazon and others found that removing 100 milliseconds of latency improves sales by 1% The idea is that there is a significant delay between hovering over a link and clicking that link. Say it takes you 300ms of delay. That 300ms could have been spent preloading the next page. And if you do use that time preloading, that page loads that much faster.

The preloaders would load the page content before users want to visit, so when they actually do, the page is served from cache instantly which would improve user experience.

What if I have more than 1 page preloader?

The fact that you need preloaders for your site, but probably only need one. No need to preload the page for a couple of times in a row. Which will turn out to waste network resources. So if you have more than 1, you should be considering to choose one active only. If not, there would a race on preloading pages on your site in the background.