Usually checkout pages don't have pesky ads galore, or any. But such a page usually has a ton of anti-bot scripts, such as captchas and other privacy-invading checks.

Ad blockers usually block such stuff, for a good reason. But I don't mind it on a checkout page specifically though, because on a checkout page I wilfully disclose a ton of my private details, such as name, address, etc.

Good checkout pages work well with an ad blocker on.