Is it dangerous to not updating apps on my Iphone?

Not dangerous, but strongly recommended.

There is no reason to not update any app. Each publisher will update their apps for a reason, regardless of it being a small performance update, feature update, or even a whole over-haul, you should definitely update your apps.

If you think it's a hassle, you can turn on Automatic updates.

Check out this article: http://savvyapps.com/blog/how-often-should-you-update-your-app