It's been about a month now since I installed BlogRush on the site.

Over the course of the last 30 days, BlogRush has sent less than 2% of my total visitors. Not exactly a windfall of traffic.

You may notice that the widget is now gone from the sidebar. Why not leave it up since that 2% of traffic likely wouldn't have arrived here otherwise? It's free traffic, no matter how little isn't it?

Well, not exactly. I look at the opportunity cost of that traffic. Sure, it generated more visitors to the site but the question is how many other people clicked away to a link on the BlogRush widget? And how many of those people came back after doing so?

If my own experience is any indication, not many came back. I have clicked on a link from BlogRush on other blogs a fair number of times, and it's rare that I go back to the site I came from even though it stays open in a window underneath.

By the time I read the new site and possibly link from there to another one, I've lost whatever focus I had on the first site.

To me the opportunity cost (the potential value they could offer if they didn't leave my site) of those lost visitors is far higher than the value of the additional ones.

That's something you should always consider in any aspect of your business. If you choose one path, what are you potentially missing out on by not choosing another? That's something you can only determine by testing, and if you don't test you could be leaving a lot of money on the table.