It seems that I can add credit to it (or at least I didn't get to a point
where it rejected this request)

but as I have to go to a specified station to "activate" that addition, this
seems a pointless thing to do given that I can add credit at a station from
the machines without the hassle of nominating a station first

As a one off, I agree. Auto top-up, OTOH, avoids having to worry about
running out of credit. Which can be a bit of a problem if you've just
boarded a bendy bus. (Not happened to me, but people have been
prosecuted for inadvertently running out of credit on a bendy bus.)

-roy