This is particularly important to freelance web developers.
A colleague of mine is so thorough with his projects that some would call him a bit anal. But no one complains, because the work rarely ever needs to go back for a second revision. I’d like to think I’m the same. Going beyond the exact scope of a task to make sure the job is done the right way the first time. Sure, it might take a bit more time now, but it will save a lot of time down the track.
We’ve gone through quite a lot of contract web developers over the past year and the predominant reason we fire them is because of a consistent lack of attention to detail. We outsource work because we want to free up internal resources to work on more important things, but if we have to fix your mistakes all the time it’s usually just easier to do it ourselves in the first place.
It’s simple, don’t rush, think about the project as a whole, and test.
If you’re a freelance web developer contracting to web development firms, you're only worth as much as the value to provide to the company. This is usually measured in time or money savings. If you want to charge $100 / hour you need to create that much value for the company. On the other hand, if you only want to charge $25 / hour, you probably don’t have to worry about it so much. Or, looking at it from the other perspective, if you’re only willing to hire a $25 / hour contractor, don’t expect to get the same value as a $100 / hour contractor.