Most current action cameras are waterproof to a meaningful depth right out of the box, which raises a genuine question for anyone considering a dedicated underwater housing: is it actually worth the extra bulk and cost, or is that a holdover recommendation from an era before built-in waterproofing was reliable.
Depth rating is the honest deciding factor
Built-in waterproofing on most current cameras covers casual snorkeling and shallow water use comfortably, and that's genuinely sufficient for a large share of what people actually do with these cameras near water. Once you're talking about actual diving depth, well beyond what the bare housing is rated for, a dedicated housing isn't optional, it's the only way the camera survives the pressure at all.
The less obvious reason to use a housing even in shallow water
Beyond depth rating, a housing protects the camera's exterior buttons and ports from sand and grit in a way the bare waterproof body doesn't, and I've had more actual gear problems from sand working into an unprotected button mechanism than from water intrusion itself. For beach and ocean use specifically, even well within the bare camera's water rating, that abrasion protection alone has made a housing worth carrying for me.
- Bare waterproofing: fine for casual snorkeling and shallow, calm water
- Real diving depth: a rated housing is not optional, it's required
- Sand and grit protection: an underrated reason to use a housing even in shallow water
What I actually pack now
I carry the housing for anything beach or ocean related regardless of planned depth, purely for the grit protection, and skip it for pool or lake use where sand isn't a factor and the bare camera's rating comfortably covers the situation. Small piece of gear, and getting the decision right has saved more than one camera from a slow, grit-related death that a housing would have completely prevented.