I have a subscription to PM -- I've had it for several years. It's expensive and sometimes I wonder if I should keep it. But it does have its advantages:
1. You get regular email updates on publishing-related news, including "books in the news." The news books is a good way to know which books you should be reading at any given time. It really helps me stay on top of the hot books.
2. I really like being able to search agents for their deals history. Not all agents post their deals to PM, but most do. If I'm unsure about querying an agent, I will sometimes look at their deal history. If I see an agent has 100 deals, then I can assume they are pretty successful. Sometimes I'll search an agent and they have no deals since, say, 2014. In that case, I would decide against querying that agent. Of course the caveat is that they just stopped posting their deals to PM, but I still find reviewing agent deal histories very useful.
3. You can search "who represents" and find out which agents represent which authors. There are probably other ways to find this info, but it's so easy to just search on PM.
If you are just looking for PM to make a list for target agents, then it wouldn't be worth the money. Despite the cost, however, I still keep it for the great search functions and publishing news.
A great (free) source of agent information is QueryTracker: https://querytracker.net. I use it to read the comments on agents before I query. The comments are very useful in terms of response times, people who had good/bad experiences. I would definitely recommend it.