Wait Ajax thank you for your reply but before you go out....
Next time you're in the shower take a look at the mixer. Look at the seal against the tiles, there's no way that's sealed correctly. And the wet area has significant water at all times.
A minor leak here can over time cause significant issues. It's also hard to identify.
And yes the area you pointed out does cause issues but in our experience penetrations also do.
Often the original plumber and tiler are not involved in the remediation. The owner contacts a builder whom we have noticed in NZ are calling for and specifying the product.
This may have not happened in your installs but is it worth the risk to not include this as an insurance against such leaks? Besides the waterproofing aspect the plumbing here can and does fail so this protects that.
I know mine doesn't leak cos I did it myself but I accept your point. Maybe I'm back in... well with one foot at least