When it's free to write, people spam. Therefore, many users ignore global feed from free-to-write (F2W) relays. But it's a safe bet that people paying to write are not spamming, so reading the global feed from P2W relays is much safer.
If you want your content to be discoverable by people who aren't already in your network (followers, maybe followers of followers, etc.) then posting on a P2W relay gives a very high probability that other people will see it.
