>>538618079
The problem when you place it so the wall blocks your team is that it gives enemies no other target to see and shoot, so they all instantly destroy the wall. Or you end up placing a wall in a narrow path and funneling your team even harder via narrower point. You place the wall as if you were to place cover for a cover shooter.
It's very contextual, but basically you place it off to the side and preferably slighly ahead or behind your team so they have some cover in an otherwise open space to push up or retreat behind while keeping the wall alive longer so it gives Groot bonus health.