Take in sides of tee can be quite simple. Most people do not have a cover-stitch machine, and therefore would rather stitch straight through the hem. This is what I call sewing from FOLD TO FOLD. If a professional alteration is required, I would recommend unpicking the cover stitch, taking in the sides, and then re stitching the hem.
However if the quicker solution is preferred, and the amount is less than 2 cm (3/4 in), a problem can be encountered at the hem line. The problem is that the side seam is folded back on itself at the hem line. This creates bulk. Stitching through this bulk, or trying to overlock half of this bulk can create a very untidy and messy alteration.
Here is a quick method when taking in the sides of a tee a small amount without having the bulky sides seam problem.
Once it is stitched down the sides, turn the garment back to the right side. Fold side seam to the back and stitch on the right side, starting at the top of the hem stitching to the end.
Finished tee with sides taken in, sewn through to hem, hem folded back and stitched down.
Happy altering
Judith Turner