I typically weigh all my animals once a month, more if in quarantine, up to a year and then weigh if/when I have some kind of concern. I do this just to monitor growth especially with smaller species that don't show big gains in a short amount of time. Take my Spotted Python for example, that little guy is growing, but so slow that if I didn't weigh him I wouldn't be able to see it. So I do it initially to track growth, and for my peace of mind. To each there own, but I agree with Dakski, I don't see an issue weighing BUT when it becomes an obsession, the "my BP only gained 50 grams this month but last month he gained 45, he must have an RI!" type mindsets aren't helpful for anyone.