Cobalion isn't a problem for SubSucker if he comes in when you have a sub up, as Brave Bird is a 2HKO and Cobalion can't OHKO with Iron Head even after Sub HP loss.
End result, you take out what is probably their only Dark resist and get +1 Attack.
I am in love with SubSucker MoxieKrow as it has gotten me so many kills. There's nothing so satisfying than getting to +1 or +2 and realising their next 4 pokemon are Gonna go down.
Dark is also a good STAB as Steels are quite rare in UU and Fighting types are weak to BB.
I've been running this set:
Adamant
Leftovers
252 HP/252 Attack/4 Defence
Substitute
Sucker Punch
Brave Bird
Pursuit
You don't really need Roost with Leftovers. Also I wouldn't have many chances to Roost what with Honch being frail and needing to have a Sub up in order to avoid Sucker Punch fail/mind games.
If you Roost instead of SuckerPunching, you risk losing your Sub and then being unable to Sucker with impunity. The opponent can Sub themselves or boost or status you while you waste your precious 8PP, or if you decide to Sub again they can outspeed and attack and ruin your Moxiesweep.
Why Pursuit not Night Slash? Well if you switch in on a Psychic or Ghost, they'll either status, Sub or switch out as they always expect a Sucker. If you think they'll status, Sub up! If you think they'll switch, Pursuit! Night Slash doesn't allow trapping the Dark-weaks so it's harder to get that first KO, and Brave Bird is much more useful if you want raw power.
So, once you seize your chance to Sub up and get a KO, it's just a matter of spamming Sucker/BB to chew through their team like paper.
Of course, Sturdy/bulky/resisting pokes have to be taken out or weakened for this to work but due to the large number of slow status users, low numbers of Dark/Flying resists, large number of Psychics and frail sweepers, and the general unpreparedness of most teams for Moxie, I would say Moxiesweeping is the strongest use for Honch.