Do you mean what is the importance of following any IBM instructions to IPL from the A or B side? Or are you simply wondering if you need to be concerned about it in the normal course of maintenance?

For the first, if IBM gives you instructions to IPL to either A or B before doing any following step, the importance is that the next step will probably fail if you don’t do it. Technically, there’s a chance of catastrophic (probably software disaster) failure.

For the second, you can usually ignore it and let the system manage it. A decade or so ago, it could be much more important; but I haven’t had to pay attention for years. (Except from explicit IBM instruction.)

Tom