What do messages do in Elden Ring?

gamepur.com:

As in other FromSoftware titles, you can leave behind messages in Elden Ring for a variety of purposes. You can use them to warn players of environmental hazards and upcoming boss fights, or notify others of nearby valuable items. You can also leave behind messages joking about elements of the game, such as its characters. Inversely, you can interact with messages others have left to read advice or jokes yourself. While you don’t have to engage with Elden Ring’s messaging system, there is one subtle function of it that might make it worth your while to leave a message here and there.

Players can choose to applaud or criticize every message they find, depending on how useful and/or funny it is. Interestingly enough, this voting mechanic can impact gameplay in a pretty big way. If you leave a message, and someone applauds it while you’re playing, your health will be restored by a pretty hefty margin. Given how easy it is to run low on both health and healing items while exploring The Lands Between, it’s possible that someone praising your message could mean the difference between life and death.

However, there will always be bad-faith players who downvote a message regardless of its usefulness or humor. Luckily, there is seemingly no penalty associated with someone criticizing your message, meaning that you only stand to benefit from leaving behind messages.