Assaults are the units that require the lesser positional care.I think with my next play through I'm not going to bother with Assault. They are the worst class by far. I just don't see a use for them. Heavies are more powerful offensively (esp against the late game robots), Support gets 3 heals, and snipers wreck. I use my Shiv for scouting. So no need for Assault at all.
With Run and Gun their effective range of attack is gigantic, making flanking really easy (and an Assault with full damage abilities and equipped with a Shotgun can fuck anything up in a Run and Gun + Rapid Fire turn) and none of their abilities really require them to be in any particular spot (Snipers obviously have many more problems from that point of view, Heavies have no mobility bonuses and a skill that needs them to stay still that turn and Supports, even with the movement bonus, have to be in the position to be able to cure or smoke anybody that needs it, so they can't run too far away).
They ended up becoming the backbone of my squads because they can fan out one turn and then cluster together for concentrated fire in the next and they are very sturdy too.