I recently bought Senior Offspring a 12-entry package on PP. She is studying in Manchester so flying Finnair makes sense for us and her, and having PP allows her to use a lounge once each way and works out considerably cheaper than paying for access to the AY lounge.
As with all these things, PP (and their competitors) offer products that suit some very well, aren’t particularly great or awful for others and represent poor value for the rest.
I very rarely need to use paid lounges because my travel pattern generally means I have lounge access by status or class of travel, but I appreciate having the back-up – partly for gaps in coverage (e.g. no MH arrival lounge at LHR) and partly because in a few instances the PP lounge is much nicer than the airline-contracted lounge. A couple of people above were talking about GVA – IIRC, on our last trip through there we were all in the absolutely crammed BA lounge, queueing to get a seat and frankly barely an improvement on sitting in the departure hall. As soon as the rest of the family left (they were on a different flight) I moved across the hall to the delightfully quiet and spacious PP offering – which was the Swiss business class lounge!