Why use a biner or Dutch clip at strap end-loop pass-through?

[Sabatier]

I've always used regular 1" nylon climb-spec tubular webbing, created an end-loop using a water knot, wrapped the tree and passed the other end of the webbing through the loop toward my hammock. Never slipped or had any problems. What is the reason people use biners or clips? Is it for flat webbing? Or perhaps necessary for polyester? Please help this noob, because I want to ditch my tubular webbing in favor of flat poly.