People use products in unexpected ways - they do things that the product's designers never imagined. I call this phenomenon "emergent use".

It's something I explain to my clients: Don't worry too much about  how customers "ought" to use your product. Instead, you must watch and learn how customers actually use it.

If you aren't expecting emergent use, you can run into problems, especially around customer support.

But if you're ready for it, it's a huge opportunity.

Scott Heiferman talks about emergent use in the early days of Meetup:

"Most of what we thought Meetup was going to be used for, people didn’t use it that way. And what they did use it for were things we didn’t imagine when we were building it." 

Be prepared to adapt what it is you think you're selling once you find some real-world evidence. Or better yet, gather evidence before you launch, through a process like Customer Discovery and alpha testing.

Don't forget to keep doing it after launch too - new emergent uses tend to emerge over time and can help you steer your product roadmap.