Curved turnouts are useful to construct sweeping curved junctions and helpful in saving layout space as stations fit much better alongside straight tracks. Whether it is to install a cross-over between tracks or to start a new siding doing so on a curve allows better use of limited space.
Curved points radii approximate to No.2 radius for the inner curve and No.3 radius for the outer curve, though the actual radii are usually adjusted to ensure the two routes diverge quickly and a couple of special tracks are needed to compensate. Peco have decided to supply these extra track pieces with the N gauge Setrack curved points, so you will not be short of the special track pieces.
When installing a cross-over use the short curved and straight track pieces to fit the concentric curve geometry, one of each is provided in each pack, so there will be one spare straight piece which can be used elsewhere on the layout. (Note, while part numbers are shown for these track piece these are not available separately.)
Templates for Peco points are available from the Peco website.