I have always cross-chained (at least to the extent that the newer outside chainrings allow) when there was good reason for it. I live to climb. I love going hard uphill. If that hill levels off briefly I don't want to have to ease up to do two double shifts to say PC for that lesser grade.
In a race many decades ago, I badly over-geared my bike, 54-44 x 13-17 for the States on a flat course. Less than 40 riders. I spent 80% of the time (maybe more) on the small ring. Rounding the turn onto the 2 mile finishing stretch, I shifted to the large-large so I could pull a surprise jump a mile from the line with just an easy shift in back to the 54-15. Worked beautifully.
Ben