I've got some spare plasma cannon guys - and a spare sergeant who I gave a badass power mace and servo skull to - and I'm planning to use them to build my first devastator squad. The thing is, I'm not sure how devs fit into my list. I like mechanized lists, I like vehicles, and I like mobility. Devastators seem like the opposite of all this: static and with no particular reason to ride in a transport. That said, I'm sure they can be powerful, and I'm not sure what else to do with those plasma cannons.
So, teach me how to devastate. What is their utility? Do they have a place in a mechanized list, or are they overshadowed by more mobile vehicular heavy weapons? Is there a clever way to make them particularly effective, or are they just a blunt instrument? What else should I do to make my Devastators effective?
Thanks in advance.