Check bags are different from carry-ons in terms of what's allowed, too. At a MINIMUM, any liquids in check bags should be in well sealed double plastic bags, so that if the bottle leaks it won't cause a hazard (or ruin your clothes). Beyond that, check with your airline for what they do and don't permit. Just as an extreme example, in the US, it's legal to carry a gun in a checked bag, but you certainly wouldn't want to try that in a carry-on -- and there are still some "hazardous materials" you aren't allowed to check (lithium batteries outside devices, for instance). Some of those can be shipped by methods that keep them off passenger aircraft, some can only travel on the ground or sea.