it is the operator that chose to set it to “enable” or “disable”.
if enable, the Ms is allowed to IMSI-ATTACH when it is switched on.
if disable, the MS will not attach. Result : it cannot get paged, cannot receive calls.
But it can make calls.
Of course, all cells should have the IMSI-ATTACH = enable.
In some rare cases, it could be useful to disable it, I guess, but I don’t have any example to give you.