Pretend we have 2 sites.
Site A and Site B.
Ive always been under the impression that if both site A and B are hosted with the same webhost, that Google doesnt like you linking Site A to Site B or even worse both sites to each other.
I really dont see the problem. Why would Google penalise a site for doing this. What if they are related? Its natural for a webmaster to want to promote their other sites right?
Do Google really penalise sites for doing this?