What it costs you in storage
The still is an ordinary HEIC. The video beside it is what you pay for, and in everyday shooting it adds roughly as much again — call it a couple of megabytes per photo, every photo, because Live Photo is on by default and stays on until you turn it off.
That is the quiet part: a library shot with Live Photo on is far heavier than its photo count suggests, and almost none of those clips are ever played back. If you want to see what it does to your own number, the storage calculator has a switch for it.
What you can do about it in iOS
- For new photos: in the Camera app, tap the concentric-circles button at the top to turn Live Photo off. It comes back on next time you open Camera unless you also switch on Settings › Camera › Preserve Settings › Live Photo.
- For photos you already have: open one, tap Share, then Duplicate — iOS offers a still-only copy. The original still has to be deleted for the space to actually come back.
- To find them: the Live Photos album under Media Types in Photos › Albums collects them, if your library has any.
What it is worth keeping
The honest answer is: some of them. A Live Photo of a child laughing or a wave breaking is the reason the feature exists. A Live Photo of a parking sign, a receipt or a whiteboard is three seconds of video you will never watch, attached to a picture you needed for an hour. The split is not about the format — it is about which photos were memories in the first place.
Kept groups the near-identical runs that Live Photo shooting tends to produce and suggests one to keep, on the device, with every delete recoverable for 30 days.