The traditional method to start crocheting in the round, is to work a few chains and join the first to the last one, with a slip-stitch. This often results in a little hole. The single magic loop solves the problem of the hole, but it is weak. The double magic loop is a better option.
Blocking projects finish them off perfectly. If you are working on a modular project, blocking the individual pieces ensure a much easier joining process at the end.
Use the first video if you are right-handed, and the second if you are left-handed.