I see a lot of cooks at NYC delis using their cheap serrated knives for absolutely everything. These guys are usually really fast and efficient at what they do. I think they use the sandwich knife because that's what they're given, and because doing everything with one knife is quickest. But I wouldn't follow their example unless working at a deli.
As far as "there are ways to use a serrated knife besides sawing," yeah, if by sawing you mean cutting back and forth. But the knife will always cut like a saw ... which is to say, it will tend to rip, rather than separate the food cleanly. This is a simplification ... under a microscope, you you'd see that all knives rip. But serrated knives do it on a macro scale that causes more damage to the food.
