You represent your company
You are a representative of your company any where you go that you disclose your place of employment. Offsite training, conferences, events your company sponsors, etc. Sometimes people will want to reach your employer and providing them a business card enables this and puts you in a positive light.
Even if jobs aren't officially posted, we've all had those moments we know there is an opening or "soon to be opening" or that our company could really use a good (insert title here). When at conferences, sometimes you happen across that unnoticed talent, or that person of incredible expertise who's ready to make a move. You chat with them and realize they'd make a great asset to your company. Sure you're not a recruiter so don't have the authority to hire them, but getting them in touch with your employer could gain your company a great asset, and likely get you a little money and good rep with your company.
Let's say your company deals in a niche market such as providing tools to disc golfers to get them a variety of interesting / useful statistics. You bump paths with someone who works for another company that deals in monitoring systems for disc golf competitions. You don't have the authority to negotiate anything, but it becomes obvious a mutually beneficial relationship could be struck, so once again you pass on your card and promise to talk to (appropriate party) where this could become a lucrative relationship between your companies.
You may not be in sales, but it's still not a bad idea if you here someone complaining about something that your company offers a product to fix make the sale. Explain what you company does and offer them the card if they think they might be interested. Again when your company gets that big sale and when the person says "yeah, I bumped into your employee (name) at a conference and he told me about (product)" you're helping your company, and they know it.
It's actually about you
So why take the time to do all this when you don't get commission, etc? Simple anytime you do something that makes you a more valuable asset to your company you improve both your job security and better situate yourself for consideration of promotion as well as raises. (Plus you can always jot your number down in the event the connection is appropriate to be individual, such as another application developer on similar tech who seems to be a great resource to sharing research on new tech, common pitfalls, development ideas, etc.)