Channel sections have a shear centre off the web and on the opposite side as the flanges. This makes channels difficult to load without inducing torsion. As such, channels are often used as beams in applications with frequent lateral torsional bracing.
Things to like about channels:
1) Their nominal depth is their real depth. This simplifies detailing sometimes.
2) The flat side is easy to connect too. They make great stair stringers.
3) They make slick single member tension only cross braces and RTU frames.
4) Laid flat, six and twelve inch channels can be set into steel roof deck flutes so that you can stack heavy things on roofs.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.