once is far more traumatizing to it than lots of smaller cuttings. If it is yellowish when you cut it then you've waited too long. Why wait until the whether is hot before you start stressing your grass?

You're also missing a good opportunity to get your lawn growing thicker. Thicker lawns retain water better in the hot sun. Grass doesn't get thick if it's growing tall. It has to be cut before it starts thickening.