TB can be reactivated, bacterial infections
can become life threatening, and some viral infections
that should be mild can become life-threatening.
I do not think, but am not sure, that once a week at the modest dose of 20mg would be that suppressive to the immune sytem, leech calcium from the bones, nor make you severely steroid-dependent (from the adrenal gland perspective). But, there are other things also to consider.