Some people seem to think that since this question is about the security of Steam vs. non-gaming software, it's on topic. But the question is asking a general security question, as Arda Xi put in the comments: "This is really just a question asking for the advantages of two-factor authentication."
I believe this is fully outside the scope of what we should be answering here on gaming. This question, at its core, has nothing to do with Steam, and therefore nothing to do with gaming.
If this question is allowed, where do we draw the line?
- "What are the pros and cons of using a strong or weak password in my gaming platform?"
- "What are the pros and cons of riding a bicycle while playing games on my gaming platform?"
- "What are the pros and cons of eating salad while I'm using my gaming platform?"
Ask about options in the platform, fine. That is within our realm of reasonable questions. But asking about completely unrelated topics that you happen to also encounter while using the platform should be off topic.