I used to do ALL of my quilts tied, my mother always tied. because its faster? cheaper? I dont know. since I have learned to hand quilt I still often tie, because they just turn out different... more cuddly, less formal.
Oklahoma Suzie has it right! square knot! and use a strong yarn, like red heart. yarns that feel soft tend to wear badly and fray weird.
tied is especially good for beginers, my first quilt with triangles is tied and NOBODY will ever know that my points dont match