A developer won't be handling the design themselves, but a designer might well be contributing some code on the front-end. And it's sometimes the case that such code isn't well (or consistently) formatted, or is too complicated, as writing code isn't the primary aspect of their job.
It's like poorly organised PSDs. You might be totally fine littering your file with spurious layers, bad names, and inconsistent groupings. The person you might share it with won't feel the same way, and it'll compel them to waste time figuring it out and possibly spend more time making it sane.
But for personal projects where a developer might want their own site, the advice here is good.
Sane organisation, attention to detail, and knowing what looks good and bad all come under this, I think.
Tip #2, give up on pixel perfect designs
In the domain of fine art, the area between elements is called negative space,
although in other areas of design it’s often referred to as “white space.”