The AGPL is an open source license: you give people access to your source code and they're free to modify it and redistribute it as long as the code stays under the same license.
The main (only?) difference with GPL is that providing a service based on AGPL code is considered the same as redistributing the software so you can't make proprietary changes to the code and say "but I'm not redistributing the code, I'm only running it on my own hardware so I don't have to make the source code available" as you can with GPL code. I believe the OSL3 allows protection from that too btw.
Businesses are still free to take your code and provide a service based on it, they just have to contribute back if they make changes which seems only natural.
Just like the GPL, it's there to ensure that the code stays free. It's only plugging a loophole which makes the GPL less relevant in the age of services.