First baby took both breasts mostly each fdg.  Second baby took only one from
the beginning (mostly) and still does at 10 mos.  Both were/are thriving,
chubby, healthy babies.
I'm for letting the baby decide.
If mom wants to stockpile milk for future use, here is the opportunity to
express the milk from the "unused' breast.

Laurie Wheeler, rnc, mn, ibclc
violet louisiana