Snoozi soozi originally I cut myself two bias calico strips so both sleeves could be done at the same time, then last year I decided to make myself four new shirt type tops, of course in different colours, so I was trying to be more economic with my time, and as I was using more than one machine plus an overlocker, I cut myself some more, so when preparing the sleeves, they were all treated to this calico bias strip at the same time. (yes I get through quantities of calico in my toile making!!)
When I have finished with them, I just roll them up in pairs and they sit happily in the corner of a box waiting for the next outing.
I agree with you it does look like magic and indeed it is magic, and I haven't been disappointed yet. By the way I also sew my sleeves in using a triple straight stitch, this is a super stitch it goes forward one stitch, then back over that stitch, then forward again over the two previous stitches - so there are three on top of one another, before moving on and repeating the sequence again. This has plenty of give in so you should run no risk of having an armhole seam popping. This stitch can also be used especially on the crotch seam of trousers, and in fact anywhere where there is likely to be strain and the risk of popping. BUT be warned, trying to unpick this stitch is near impossible and will drive you crazy. Have a look at your stitches on your machine and see if this stitch is there - I have used this stitch hundreds of times on both adult and children's wear and haven't had it pop once. If you have this stitch, grab a piece of fabric, fold it so it is double and stitch a line, then also stitch a line on the bias - then give the fabric a good tug and see if it will pop, also try an ordinary row of machining - nothing fancy just plain straight stitch, and then another using the triple straight stitch and again give the fabric a good tug and see what happens.