A client’s goals are important. If they want maximum strength and hypertrophy, I’m going to have them lifting weights at a level that’s challenging for them. However, we live in tri-planar motion, so even a person who wants to get bigger and stronger can benefit from tri-planar training.
Personally, I’ve gotten away from “functional” training because it’s so over-used and generalized. I like to use the term “triplanar” training to indicate that I’m challenging each joint in all of the planes that it stabilizes and moves. Multi-joint, multi-directional. Not as challenging from a “heavy lifting” sense, but very rich in a proprioceptive sense.