Saddle stitching is the way of binding where the pages are gathered together, folded and stapled along the crease from the outside cover, to create a book.
With perfect binding, the inner pages are placed together and glued along the spine with the cover applied at the same time. When the adhesive dries the pages are secured firmly in place.
It all depends on the weight of paper you use, but the maximum you should really saddle stitch is a 60 to 64 pp booklet. Anything with a page count above 64 pp should be perfect bound.