That depends. If you are just saying "use my product" that ruins the internet. However if you give detailed helpful responses to questions in general that can be helpful.

You can be as dishonest or helpful as you want. Back when google did organic ranking a lot of communities thrived on forum signatures. If you have thousands of helpful posts others know your level of expertise.

But this is something that is completely missing with these Reddit posts. Most are spam.

Its to easy to join and to hard to have dialog or ban users on reddit. It has kind of one single standard while with forums it depends a lot what the topic is. If people are building something together you need to be a productive participant before you can make fart jokes or complaint about your hangover. Accademic forums often had zero tolerance for bullshiting in serious topics. If your reply gives away you didnt read the article you deserve a warning.