I am not a big fan of this. I dont mind partial successes or degrees of success, but if you are talking about adding in unrelated elements to the roll (i.e. I failed my parking roll at Shaw's today, still managed to get my spot but had to dodge a tumbling boulder as I stepped from the car). I have seen games that handle something like this well, but usually what i see when people discuss it online, is using it to add in new complications (like indiana jones getting the treasure but then a group if angry warriors appear).
I think there are many completely related results that don't fall on the usual spectrum of failure, partial success, or success. Examples:
(1) unintended success, like trying to shoot the gun out of someone's hand, but hitting them right between the eyes instead - or you are researching one question and fail to answer it, but make a discovery you didn't expect.
(2) extraordinary success in some aspects, but failure in others - such as if you complete the repair in half the time, and it works as intended but will give out soon.
(3) negative consequences of extraordinary success - like you run someone through with your spear, but your spear gets stuck; or you dodge out of the way of the grenade, but fall into a ditch.
In my experience, the usual rules for partial success don't handle these cases well because there is an expectation that a partial success is uniformly worse than a full success.