It's been an integral part of every Puppy I've ever examined. BarryK conceived of the need for this well over 15 years ago.
It lets you install a Puppy, customize it with any apps/utilities you want, different appearance, etc, then create an ISO image of your Puppy in its current "state-of-play". Plenty of Puppy users want to be able to boot an identical setup on whatever machine they choose to use, without the use of a save-file/folder to hold their customizations.
The one downside of this is with any browser you may include. Browsers, as we all know, very quickly become outdated as online exploits are discovered and made use of by unscrupulous individuals. However, with the range of 'portable' browsers I've developed over the last few years - with the invaluable assistance of many other Puppians - this is easy enough to get round, by running said portable from a suitable flashdrive.
The 'zilla-based ones invariably have their own updater mechanisms included OOTB. My Chrome & Edge for Linux builds have an updater which I've scripted for them, so these can be kept up-to-date when you're notified of the new version.
It's one of those things, re-mastering. It's all a question of personal taste, and what the individual user wants to do with their machines/operating systems.
Mike.