So, the nominated First Officer will continue to log all the flight time in his personal flying logbook irrespective of whether he is in the operating seat or not. If he is lucky enough to be rostered as the nominated First Officer on a series of 4 pilot sectors he could in theory operate up to 150 hrs in 28 days.
In effect, for the purpose of licensing, promotion, command, etc, he could be logging up to double the "real hours" that he has actually operated. 75 hours or so in the seat, yet 150 hrs in the logbook. That could be up to 1350 a year! Interesting concept, lots of extra "free" flying time and credit time to boot. A double bonus and no doubt welcome by some more than others.