If you're running a race, moving the finish line 5 feet closer to the starting line or moving the starting line 5 feet closer to the finish line accomplishes the same thing.

Adv/Dis vs DC works the same way. The only difference between the two is the level of granularity in the adjustment and whether or not the player is aware of the difficulty of the attempt. Adv/Dis announces that something is mechanically difficult or easy before a roll, and a DC does not.

This changes if you are dealing with a rewritten scenario, of course - as they predefine the DC, but if you're deciding on the fly then there's no real difference other than the power of the adjustment since Adv/Dis is limited to around +-5.