FB has no shelf life, not that the content isn't there it's just not easily searchable like a forum...
That may be true from a client-side perspective but not from a data mining perspective. Everything is archived and indexed and available to third-party business partners. If the platform is free, you are the commodity. Most use cases are not nefarious and most data is anonymized to a certain extent.
All of that being said, firms like Forrester, use every bit of data they can collect to build multi-axis profiles of you. And sell that to anyone buying.
We had a presentation from them about five years ago where they showed just how accurate they are with there profiles. Data from Visa-Mastercard is combined with public records, credit reporting, business registrations, address, super-cookie data, social media content etc.
They told me all about my buying habits, how often I go on vacation and to where, my income level, how many businesses I had opened, family size and demographics... You name it, they knew it. All of this based on one index, my address.
This data is used by businesses to understand who they are marketing to. They run scenarios to see how potential changes in rates (in this case it was for insurance) would affect sales. For example, if they market via Facebook for customers and target x-profile the risk level is x% decreased. Now if you tune the message for cost or benefit, or social good you see x% higher return. All of that is fairly benign. They just want to market to the "right" people.
Where it becomes an issue is when someone's motivations are bad. The more data you share the worse the potential issues. Keep in mind bad actors can get anything and everything about you at will. Your SSN will cost someone $3.50. That is an accurate number as of four years ago. The only reason you are not targeted is there are billions of people on the planet.
I stopped with Facebook years ago after the terms of use changed. I do miss out on a bunch of stuff as a consequence but I am glad I did.
As an example of what can be done, I have been looking for property for a number of years and every time I find one. I start with research. I am just searching public records trying to find the motivation for sale, how much is owed, etc. Nothing harmful, just trying to see if they are motivated to sell. Even when people are older and less likely to be on social media you can still find them, understand what business they are involved with, how many homes they own and where, the relationship between them and their kids, their kids marital status and possible selling motivation from a divorce of the kids... A real use case. It is all out there.
Bottom line. Think twice about any piece of information you share. Taken in aggregate it still builds a profile that can be exploited.
And lock your credit.