Advice needed on registered users.

I am running MultiSite with ProSite plugin and have allowed free subscriptions to users so I may moniter my new site and how it is working internally before moving to paid subscriptions. I now have a number of registered users and some with the same I.P adresses but all empty sites apart from a few Groups created with some content and links to other sites and no other activity. I need to know if this is ok for my site to allow or is this potentially damaging to my site in terms of rankings, Google, bandwith, disk usage etc etc?
Advice would be greatly appreciated here.