I am not talking about links on porn websites to non-porn sites. But suppose some really old blog (blogspot? ) , nofollow, pagerank 0, that is not read by anybody, and not in your topic would the value of a link like that be 0, above zero, or a negative value? And if its above zero, how many links like that would be needed to see any actual difference? While at it, I wanted to ask if it makes any sense to leave blog comments with a link to a parked domain? Does google adsense allow referred traffic to domains?
Values of links differ and there are some of them that are really helpless in indexing point. However every link increases the whole popularity of your site and might lead more people on site.