If you have a lot of information for your role-play (and you should), it seriously behooves you to at least distinguish your sections in a way that is easy on the eyes, flows, and can be easily discerned through a quick skim. A wall of text where the only thing distinguishing headers and body paragraphs is a bold font will be considered a daunting read and can easily be off-putting to the point that someone skimming may be disinterested because key information is not readily available to them.
Meta Journey's Hub uses minimal CSS (colored headings and padding) and information is easy to find in clearly labeled and separate sections.
Cornered On The Market has a lot of information to portray: the OOC overview of the role-play in the first post, and in the second, IC information in one portion and art stuffs in another. All three things are separated and are easily distinguishable from one another through various means (portion header, color-coordinated). In addition, information within each portion is clearly separated, and for convenience, the portion header has targeted links that take you to a specific section of that portion for easy in-page navigation. While it could be considered a more advanced code for CSS, it is not necessary as it is for the sake of convenience.
Those are two opposite ends of the spectrum, but they both accomplish the same thing effectively. Even your
Demonic Core interest check utilizes CSS in a simple but elegant way, and makes it more appealing to read.
As the Game Master, your OP needs to be accessible to everyone, and that does involve formatting.