Crease adds perfectly sharp creases to T-spline edges.
To control the tangency of a creased section to the rest of the surface, use the tangency handles. Use Edit Form with the Vertex selection filter to display tangency handles. Use UnCrease Edges to remove the crease and the tangency points.
Like all T-splines control points, creased control points influence the surface within a two face region. This means if only one edge is creased, the next two edges in the loop will be partially creased, and the third edge away in the loop will not be creased at all.