A seat that is not held in place properly can be dangerous if not at least uncomfortable and annoying. Newer and better designs of the piston style seat post have minimized all forms of wiggle and seatposts with actual adjustable pistons built into the post are even available.
An unstable seat can be perilous if it is merely inconvenient and frustrating. Contemporary and advanced designs of the piston-style seat post have minimized all types of movement and seatposts with integrated, adjustable pistons are now also available.