this is actually true, but the tricky part is when it comes to the collar, hemline..for that you need a serger, a regular sewing machine wont do it for you
Not necessarily. You need control at the neckline and hemline, otherwise it would stretch out. If you notice on knits, all of it it done on the serger. It's a quicker way to sew and finish a seam without having to do extra steps. The seams on woven don't stretch if they get sewn on a serger.
A serger doen't really do much, but match the characteristic of the material.
Check the hem of your mas produced tshirt. The hem is not done with a serger, but with another machine called a coverstitch machine that produces 2 parallel lines with a zigzag on the reverse side. You can sort of replicate that with a double needle on you regular sewing machine.
To handle the neckline, it would be smart to use a serger simply because it would be easier to finish, there wouldn't be any folding over and stitching business or facings.
Alot of success is just based on trial and error and finding the best technique for your particular fabric. I have 2 sewing machines one straight stitch and another with zillions of stitches, and I normally reserve the zillion stitch one for silks and really lightweight fabrics because it handles it better and I have better control over it.
My straight stitch machine is a pure workhorse so I can take like 6 layers of denim and it will do the job. That machine can take a beating so it I use crazy fabrics for that one or if I really want beautiful topstitching.
My serger I use on knits, or if I don't feel the need to use nice finishing techniques such as french seam, binding, etc. or if I'm pressed for time and need to make something quick. It barely gets used, but when I use it I'm very happy that I have it.