Imagine holding an open house and when prospects
arrive, your assistant promptly directs them to another
open house down the street without getting any
information or without asking any closing questions. You
wouldn’t end up with very many leads at the end of the
day, would you? In another way, imagine being a fisherman and using a
fishing net with a bunch of holes in it. You might know
the best fishing spots but in the end you can’t keep them
because they fall right out of the net!    
That's how many of today’s websites are designed!

My number one rule and most important concept for your
own website has to do with keeping your viewer within
your own environment. It is absolutely crucial to not
allow them to leave until they have responded. Of course,
they can always close the window, but if they are there
because you “drove” them there and they want pertinent
real estate information, then the result should be an
inquiry about a property or service that you offer. Many
of the major real estate website makers break this rule to
the detriment of the agent or broker.
So the point is to eliminate the “holes’ in your website.

What is a hole?

      An example of a hole (like in the fishing net) is where someone comes to your website and clicks on a link that takes them to another site (where, many times, they make their inquiries). Some website providers have tried to solve this problem by “framing” the linked site within the agent’s site. The problem is there are sites that are programmed to open in a new window, therefore canceling out the framing effect (such as MSN Homeadvisor).  

Another problem with framing a site is that when they click on "more information" or some other link, many times it is within that framed site so the lead goes to that site anyway.

Real estate is a sales-oriented industry. Each agent
depends on “leads” to survive. If someone comes to an
agent’s website and just looks at it and goes away, the
agent gains very little. Where the agent and broker benefit is to have that “prospect’ send in their contact information so the agent can get back to them and close for an appointment. Then a sale can be made. That won't happen if you are linking them to other sites...

So, my recommendation is not to link to outside websites
unless they are definitely not going to sell space to your
competition (sites such as government sites, non profit sites, etc. are usually O.K.) If you are involved with a brand, be careful how you link to your brand site or the lead might come back to you at a price. Bottom line: IF the content is good enought to link to from your site, it is good enough to have ON your site.