[EinarRhys]

As Mush pointed out that there are rules in Soul Society and certain kidou cannot be used. I believe that certain kidou are relatively useful and can be used for evil purposes. In order not to have members learning them; I think the Soul Society forbids teaching or practicing them.

For example:

Jikan Teishi could be used to take a part of soul society lets say if someone infiltrated the confidential part of the library. They could use that technique and take a chunk of the library with all the books and escape. The other possibility is that it's relatively easy in battle as well and in stealth missions as well. o.o