Most table saw inserts have wide throat openings around the saw
blade. This makes it all too easy for narrow cutoffs to fall in the opening and
possibly bind against the blade. In addition, there's often chipout along the
bottom face where the workpiece isn't supported.
To solve these problems, I like to use a zero-clearance
insert. But as you can see in the drawing, the one I use doesn't replace my standard
table saw insert. Instead, I use a large piece of ¼" hardboard that rests
on top of the table saw.