It's not competitive at all, but I take them because I love the Idea of a Chaos lord (King of Badassery) and a retinue of madmen in terminator armour (his Squires of Ass-Kickery) chopping stuff up.
hahaha, ^^this. My favorite Lord is a Terminator w/ combi-melta and Daemon Weapon. Why? Because I grew up with the Chaos Dream, where a Lord could make his own way, make is own warband, and not be stepped on by Daemon Princes (who are part of the SYSTEM, MAAAAN)