Formal vs. Informal
Obvious example: you likely won’t need to take on a “sales pitch”-style tone for a student who’s already enrolled, so there’s no need to list flashy statistics about your program, platform, or anything like that. Get to the point, and focus on what you need to get across. More than likely, visitors to the Portal are searching for a specific bit of information. Don’t make them work to have to find it. Give it to them, and get out of the way.
This is especially true in situations where you’re presenting information as an authority or for when it has to do with legal matters. In these cases, it’s best to err on the side of caution and stick to a formal tone. What you don’t want to do is have your reader take your rules or guidelines as suggestions or opinions when they are, in fact, the law.
All that being said, don’t be afraid to let your own voice shine through when you think it might be appropriate. It’s entirely possible to deliver a high volume of content while staying casual and conversational—much of this style guide is written exactly that way!