When do you use 12 inch spacing for stud walls?

One of the main reasons to use studs 12" on-center would be because of the load they are carrying. If an unusually high load is placed on the wall, that could be a reason. Another could be a high or tall wall that it exposed to wind loads. A wall such as that may need close spacing to comply with building code.

Studs should be spaced 16 inches apart on center. Because of the dimensions of the sheeting, the first stud should be placed 15 1/4 inches from the end. This ensures that the sheeting will land exactly in the center of the fourth stud. Some studs can be spaced 24 inches apart if the wall will not be load bearing. Twelve inch spacings (to centers )is used for additional support around door ways if there is reason to believe that there walk way will be have high traffic, if the wall is an outside facing elevation where whether conditions could impact on the structure and some use 12in centers near Windows to provide a more stable structure. - In general building codes for your area and/or country will be required to be followed as codes are not international.