Depends on the housing.
First, definitely remove the o-ring. That way any pressure differential inside the case (plane cabins aren't pressurized to 'sea level' in most cases, and if you have to check baggage obviously pressure is even lower in the compartment) won't push the o-ring out of the seal and risk damaging or stretching it.
As for the camera inside the case - for point and shoot it's probably not horrible as the OEM cases are pretty form-fitting. Although with the o-ring removed there might be a bit of rattle. For DSLR's its usually not recommended since they 'screw' to a tray base with the tripod mount threading, and having that suspended inside your case may or may not be sufficient support for the weight of the camera in case of a dropped bag.
I usually 'pack' as much stuff as I can gently fit 'inside' the housing - ziplocks with o-rings and spare o-ring grease, zoom gears and the like - so the hollow interior space isn't totally wasted volume inside my checked bag. But I don't put the camera in it.