When Drywall Thickness Matters
Drywall thickness can sometimes be important in terms of the particular application, while at other times doesn't matter a great deal. In most locales the building codes may not specify a particular thickness that is to be used, although it isn't uncommon that the code will specify a minimum allowable thickness.
Most, if not all drywall, comes in one of 4 different thicknesses, 5/8", 1/2", 1/4", and 3/8". When people refers to a standard drywall thickness, they usually mean 1/2" thick drywall, though once in awhile you'll see 3/8" identified as the standard thickness.
If you are doing your own drywall project, you're usually free to select your own thickness, though if it involves patching, adding or replacing existing panels, you'll of course have to use the same thickness that is presently there.
Thicker Often Better, But Heavier - There are some tradeoffs involved. If there weren't, all drywall would probably be of a uniform thickness. The thinner the drywall, the easier is usually is to work with, mainly because drywall is a lot heavier than it looks. Someone who could manage moving a 4' by 8' sheet of 1/4 drywall around, might really struggle with a similar sized sheet of 5/8" drywall, the latter thickness making the sheet more than twice as heavy as the former. Using thicker drywall for ceilings may be to your advantage as far as insulation and soundproofing are concerned, but two people will be required to lift the panels, and a drywall lift may even be needed, and the use of such a lift is usually recommended. Thicker drywall also has an advantage in that it goes flatter against the wall studs than do the thinner sizes.
Although 4' by 8' panels are the most commonly available, 10' and 12' panels are also available, and for some uses may allow a project to proceed more quickly, although admittedly for any thickness, the 10' and 12' panels are going to be significantly heavier to work with, though this may not be a problem if only walls are involved.
Standard Drywall Thickness For A Reason - Anytime drywall is installed, the thickness needs to be compatible with the distance electrical boxes for switches and outlets protrude from the studs in the wall or ceiling. These boxes usually have markings on them, and are installed such that the markings are flush with the interior wall side of the studs. If you are going to be installing 1/2" thick drywall, you'll want your electrical boxes protruding 1/2" from the studs, no more and no less. More than one do-it-yourself drywall installer has neglected this very important fact, only to find out, hopefully before the project is finished, that the switch or outlet boxes either stick out too far, or are recessed too far.
Think Green - Any general discussion of drywall installation should mention a few words about moisture proof drywall, often referred to as "green" boards, because of their color. This is the drywall you'll want to use in areas around baths and showers, or in basements which are apt to be damp. Green boards are almost always used in the walls immediately around a tub or shower, and in the ceiling immediately above a shower. More than one builder or renovator will do an entire basement, walls and ceilings, using thicker green board, resulting in a quieter area, which is also unlikely to become damp.
If you don't want to obsess over drywall thickness, and are content to go with the flow, you'll be best off using 5/8" panels for your walls, 1/2" panels for your ceilings, and purchasing a few green board panels, maybe only one or two, for critical areas in a bath or utility room.