That's such a weird strategy, especially since the remainder of the article after that comment discusses deciding a fair market rate. If a lot of your clients know each other, don't you think that one of them might get upset to find that they were charged twice as much as another? Might they think that they're difficult to deal with, or think that you're scamming them or making up hours? And doesn't this complicate your accounting?

Pick a rate and keep it the same across the board, with two exceptions... First, reward longtime clients by being conservative with rate increases (i.e. offer them a lower rate for an additional six months after you've raised your rate, and don't hesitate to tell them that you're doing it). Second, provide nonprofits/artists/etc with a discounted rate. They are usually great clients that are flexible, gracious, and allow you to exercise more creative freedom (especially if they know that they're getting a discount).

Also, you can avoid the dangers of overestimation and underestimation by providing a flexible estimate. For example, if you can typically do a website in 20 hours, but this site might take a little longer, tell the client that the estimate is 20-30 hours. So if you're charging $75/hour, the estimate is a range between $1500-2250. Instead of getting worried about quality due to an estimate that's too low, or worrying about their budget due to an estimate that's too high, they will initially zero in on the median cost of $1875. They will see the low estimate as a possible way to get good work without spending a lot of money, and they'll see the high estimate as "reassuringly expensive" (i.e. you can command decent project fees because you know what you're doing).