mozilla-services/android-sync — comment on commit e55336ef851272da6aea69a9ed8aae6996b54cd8
File: src/main/java/org/mozilla/gecko/sync/repositories/android/AndroidBrowserRepositorySession.java line 538
By rnewman:

That's deliberately ambiguous; it depends on the repository itself. The only consideration is "do we want to upload this again?". The similarity between most of the repositories is that the record will be largely unchanged from the one we downloaded.

Typically that'll be equalPayload, but not necessarily.