What are good reasons to lead dummy's first bid suit?
A couple of reasons


You have a singleton in dummy's suit.
You hold, say K8, in dummy's suit, and want declarer to commit to
    finesse in that suit/some other line (i.e. refusing the finesse), on
    the opening lead. You do this by leading the deceptive 8 (feigning
    singleton 8 or 8x). This has actually happened, with success, on real play.


The reason of cutting off dummy's communication is good, but unlikely to come up on the opening lead. Leading dummy's suit can lose a much needed tempo, especially when you are not even sure if the suit is solid etc.

Breaking up a squeeze on the opening lead? Well, if you can do that knowingly, you should play bridge for money :-) I guess it is theoretically possible, though.