When you combine or link accounts, you will be able to freely transfer your miles between the programs until NW WorldPerks dissolves completely at which time all of your miles will transfer to your DL skymiles account.
There is no charge to transfer miles between your DL SM and NWA WP accounts.
You will be able to make award bookings therefore on both nwa.com and dl.com
If you link the accounts yourself, you save DL some work...and so they reward you with 500 bonus miles.
The other information (you had asked if it was outdated): The answer is, yes and no. You cant use your SkyMiles to make a reservation on NWA.com. BUT you can transfer your SkyMiles to your NWA account and THEN make a reservation on nwa.com (and vice-versa).
The bottom line is: If you have the time (it only takes a minute), link the accounts. At the least it is 500 free miles.