This technique is super helpful then you run out of yarn in the middle of a row and do not want to tie a knot in your yarn!
You can also avoid having to come back later and weave in ends in the middle of your project.
This is perfect for afghans, but I wouldn’t do it if the join might end up in the front of a sweater. It might be ok on the back of a sweater or on a hat. You have to be the judge of that because it does make a slightly bulkier spot in the yarn that might be visible with different types of yarn.
Give it a try and let me know how it works for you!