Alright, besides the cutting function, how is it different than an overcast stitch on a sewing machine?[/quote]
The sewing machine only uses two threads, the serger 3, 4 or 5 so it's much sturdier. The sewing machine doesn't trim the edge of the fabric so you get lots of "pokies", especially after washing. The serger encases the edge after trimming off however much you need to trim (just shaving it if you are edging, more if you are sewing two pieces together with a seam).
A seam on a sewing machine takes three steps - sew the seam, neaten one edge, neaten the other edge. A seam on the serger is done all in one. The only difference is that you cannot press open a serged seam, you have to press it to one side. Alternatively, sew the seam on the sewing machine then neaten each edge on the serger - neater and longer-lasting.