First issue with this is the usage of the word "mob". In gaming, a mob is not a group of creatures, which it appears you're referring to it as. This will confuse your readers. In gaming, MOB is short for "movable object", and would only refer to one creature individually.
"A pack of 8 mobs" = a pack of 8 monsters
"Boss mob" = a ?? level monster
Getting into your questions:
Cleave is a supplementary skill. It, like Heroic Strike are off the GCD, so you can use it in conjunction with your other abilities. There's no reason, if you have the rage for it, not to use it along with TC, SW, SS and devastate. If you run heroics primarily, go ahead and glyph it if you want. If you're a raid tank, don't. There's no reason not to use it if it does not interfere with your higher-threat single target and aoe abilities.
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