My opinion, it increases the level comparison between you and the lock you are picking. ex. You're level 40, but need to be Level 45, and AL adds +5 levels, so you can now pick it.

That's completely made up for example's sake, but I've had non-AL thieves that couldn't pick nearly as many locks (ie doors, chests, etc), as my AL thieves. I'm sure skill % figures in there somewhere, but I'm not nearly number crunchy enough to tell you that.

At Hero, with AL, there are still a good number of picks that have been made to be unpickable. Usually a prep, big gold, or Nice eq chest, that you must have the key to get into. Of course those keys are usually held, not just in the inventory (or what would be the point, really).

-Cassman-