- you don't know how many times you have done the quest (unless you are doing it now and press the XP button)
- after you finish the quest on Elite you don't know whether you have finished that quest on Normal or Hard (unless you are doing that difficulty now and press the XP button)
- when you play on all 7 servers you definitely forget how many times and on which difficulties you have finished quests
Of course, it's not a problem for Favor, but it is a problem for XP.
Additionally it will help you to avoid quests with already Ransacked chests (at least in the first time of Ransacking, which happens after 8 times of opening that chest within 1 week).
For example, if you have done Redemption quest 1 time on Normal and 2 times on Elite then pressing P instead of this
Redemption --- 1 Solo/Party --- The Coin Lords --- Elite --- 9
you should see this
Redemption --- 1 Solo/Party --- The Coin Lords --- Normal (1) Hard (0) Elite (2) --- 9
Redemption --- 1 Solo/Party --- The Coin Lords --- Normal (1) Elite (2) --- 9
or any of these short versions:
Perfect Quest Window