I know both. I have family members who smoke routinely for basically their lives. You would never know, they don't let it interrupt their life. To them it is more like coming home and having a glass of wine and relaxing on the couch with a good book.

I also know and lived with roommates for whom marijuana was a real problem. The kind of person who would smoke every day, even coming home on their lunch break and taking some bong hits. I've seen them get fired from work. I've seem them completely disregard the things that need need done. I've seem how irritable they can be when they're not blazed. They may not be chemically addicted, but they surely feel as though they need to smoke for whatever reason.

None of this is to argue for or against, but the "harmless marijuana" trope is a little much. Any substance will be abused by some and will cause harm to some.