Sometimes when flights are really cheap, you can earn more PQP booking with miles vs paying money. However this basically means your redemption value for those miles was quite low.
People also calculate redemption value differently. People recommending you book premium intl using miles because paying would cost thousands of dollars. IMO this is only true if you would have been willing to spend those thousands of dollars if you didn't have miles, otherwise, it's only worth however much you would have been willing to pay for the trip (a number far lower for me). So it depends on you.
I'm always worried about not having enough PQP at the end of the year so I'll try to find good deals using miles for end of year trips I know I'm going to make. Thanksgiving Xmas visiting family, etc. I can always cancel if I end up short.
These days, because of all the extra PP I have, I've been buying more intl trips so my total PQP for the year has been quite high. In the past, I'd barely my 1K so I'd pretty much never use my miles.
But maybe I'm not so smart because I have almost 2MM miles saved up. My thought was that there will come a day where I will no longer be able to maintain status and I'd burn my miles then. However, through years of massive devaluation, I'm sure I've lost lots of value. So when you decide whether you want to value status or miles redemption value, don't forget about devaluations.