Question for Hakaa users

Do you only feed on one side at a time? I'm confused about whether this truly is to capture lost milk like I thought or if it's to do a more passive milk collection from the unused side during the feeding. I don't really leak that much and with seeing these posts and comments about women collecting tons of milk with it, it makes me wonder if I should use it? Mainly because I feed on both sides at each feed and I would not want to pull milk from the second side before she eats.