Akamai does not come right out and say it, but the reason NetSession is installed on your computer is to allow them to use your computer to "upstream" content to other users. By installing NetSession, you are allowing Akamai to use your idle bandwidth to upload files to other Akamai users.
Untangling some of the statements from: Page Forbidden | Error 403 | Akamai
"The information that Akamai does capture is similar to a web server and that information is utilized for troubleshooting and network performance monitoring only." That means that NetSession continually sends information about your computer to Akamai.
They say that NetSession will only use your computer when it is "idle or utilizing minimal network resources." That means that NetSession is constantly monitoring your network use, and sending that information to Akamai. And since bandwidth usage varies from second to second, that info must be sent up to Akamai a lot. Wait a minute, didn't they just say they only captured the sort of info that web servers capture? Web servers don't capture info on bandwidth use. What other information does Akamai capture? I could not find any specifics on their site.
So if you install NetSession, you will be joining a peer-to-peer network, and allowing Akamai to deliver files from your computer at times when Akamai deems you to be utilizing your bandwidth minimally.
I also have a security concern about the files I am receiving from NetSession. It seems like it would not be difficult to download a file using NetSession, modify it to carry a virus payload, and then leave that computer idle, and wait for NetSession to transmit the infected file to other NetSession users. I would hope that Akamai has taken steps to address this concern, but I can't find any information on that.