Does the ‘filing date’ of the visa bulletin matter to family green card applicants?

The short answer is ‘no’.

What happens to applicants going through consular processing?
Applicants who go through consular processing have to wait for a ‘welcome letter’ from the National Visa Center before they can access the ‘consular electronic application center’ and start filing.

What happens to applicants going through adjustment of status?

Applicants who go through adjustment of status cannot use filing date to file. They first have to look at a specific section of USCIS web site to determine whether or not they can use ‘filing date’ to file. It turns out that, except for a brief period of time between October 2016 and December 2016, the answer to that question is ‘no’. In other words, applicants have to us the ‘final action date’ of the visa bulletin to determine whether they can file or not.

How can applicants use filing dates then??
It could be used as an ‘early-warning’ that it might be time to prepare filing. But even that is highly misleading. Filing dates are not moved gradually over time. They move forward in bursts, advancing one month and then stagnating for 4-6 months.