If you are like me, you pick up which ever needle is handy, and it somehow manages to do the job. However there are many different needles out there, in as many shapes and sizes as there are projects to sew them with! It really does make a difference if you have the correct needle, both when hand sewing and using a machine. Here are some helpful online guides to different needles and what to use them for.
Coats Crafts for hand sewing
Sew, Mama Sew guide to machine needles