The limit of this card is that you can gradually move 1 doom each turn, so the incentive is to try to "eat" as many as possible in one go when you spend without agenda advancing first.
I am thinking of a combo with Seal of the Elder Sign for Amina Zidane (She should be able to take it?), which can move multiple doom to Sin-Eater. Controllable means you can plan to be greedier with cards that could endlessly fill itself with dooms like Blood Pact or David Renfield. effect is also not limit to the asset but any card at your location, so could be cool to team up with other investigators or enemy/location doom added by scenario.
Permanent is an asset, and asset is at the location according to the rule.
While an investigator is at a location, that investigator, each of his or her assets, and each card in that investigator's threat area is at the same location.