Let's say I have 50 sites, Would it be beneficial to create a footer with links to all them on each domain?
If the sites are related and different domain names it would not hurt. make sure to not have over 100 links on any page google does not like alot of links out
What if they are different domains but not really related as far as content. One might be about fishing and another about video games.
If all the sites are on the same C class Ipaddress, the links don't get much value. Try something like this : (lets say if you have 50 sites) From first site, link all the sites from 2-26 2nd site: link all the sites from 3-27 etc etc So that none of the sites have reciprocal links
What if they are different domains but not really related as far as content. One might be about fishing and another about video games.
Who cares what google does and does not like Blah....besides nobody really knows what they do and do not like