My WR250R had holes in the rim for bead locks, and I installed Motion Pro lightweight bead locks plus some spoke weights to balance them out. I run 6 to 10 psi for trails and feel like I need them - front just as much as back. On some previous bikes I ran 15 to 20 psi and didn't use bead locks with no issues.
My daughter has a CRF150F. It has a back bead lock but not a front. The front tire has slipped on the rim. She might have ridden the bike with close to zero air, not being familiar with bike maintenance.
But that is another reason for bead locks. If you get a flat, the tire might stay on the rim for a couple extra miles. I've ridden flats for a long way with rim locks!