Originally Posted by Delta Hog

Thank you. Are they now more vigilant to make sure all bags brought onboard are within regulation size? So that gate checking is only for reasons of space, not inability to fit in the overhead?

In my memory such regulation was hit-and-miss. Often I was told "you have to check that, too big." But other times not. Once I even brought a large full-size suitcase through security accidentally (long story, intended to check it, but my traveling companion missed it) and had to gate-check it. It still fit through the x-ray machine, though.