You may find it odd to be talking about attic hatch doors as most people rarely use them or even venture into their attic. As a result, many are unaware of the potential problems they can cause.
Attic hatch doors should be insulated and sealed so that there is no air infiltration to / from the house and attic. If this is not done, there is a potential for condensation to form, water / moisture damage and mould growth in the attic when, for example, in the winter warm house air migrates into the attic. As a result, the hatch door needs to close tightly within its opening, have the trim work around it well sealed (e.g. with weather stripping, caulking, etc.), and ensure that the hatch door itself has sufficient insulation, whether the door is on the ceiling (pictured left) or in a knee wall (pictured right).
If you’re not sure about your attic hatch door, get it inspected.