Energy flow on a site is enhanced by intercepting and recycling the flow across the site.
What I find quite funny is that I used the word "energy" a long time ago to describe what others call PageRank. David Weinberger said he didn’t like this word because it made the Web sound like an organism. Well no the Web isn’t an organism like ourselves but it definitely acts like one because its interactions upon it are by organisms, us.
This energy is basically the flow of the Web that goes through your site (i.e. people entering and people leaving). As we all know, if a site has a high PageRank and it points to something of interest on a smaller site, then obviously the PageRank for the site is going to go up because of the increased interest and traffic to it.
What I found quite interesting though is that the more "energy" a larger site gives to smaller sites, the more "energy" the larger site will attract to itself. In effect, by giving, you are making yourself stronger. Why? Because it is pointing at interesting things and in doing so, itself becomes more interesting. Why do you think Google is so popular? It is because of what it points to, not because sites point to it.
Therefore, if you notice a site that is bringing some traffic to you looks quite interesting to you, then by all means link to it. In doing so, not only will you be giving your "energy" to it but, in effect, you will be recycling that energy back to yourself as the other site gains more energy and redirects back at you.