iserith
Magic Wordsmith
I think that mathematically it comes out to a +5/-5. You roll two dice and take the higher roll (or lower in the case of disadvantage). IMO, this is too much of a modifier for most rolls. It's the equivalent of the proficiency bonus of a 13-16th level character.
It's not always +5/-5 on rolls. I'll let one of the math guys or gals explain if they are up for it. [MENTION=16814]Ovinomancer[/MENTION] for example.