Show a draft to enough people and someone will ask you to fill the space. Resist them, gently. The space is doing work.
White space reads as luxury, but it is really just respect. Margins give the eye somewhere to rest. Line spacing keeps one sentence from shouting over the next. A generous measure — the length of a line — keeps the reader from losing their place on the return trip.
Density is not value
There is a temptation, especially online, to treat every empty pixel as a missed opportunity. Another module, another call to action, another thing to look at. But a page crammed edge to edge does not feel valuable. It feels anxious.
Whitespace is to be regarded as an active element, not a passive background.
Jan Tschichold
Designing for the long form
A reading theme earns its keep in the parts you do not notice. The right measure, a calm palette, space above a heading so it announces itself quietly. None of it draws attention. All of it keeps you reading past the third paragraph, which is where most readers decide whether to stay.
So leave the space. It is not empty. It is the part of the page where the words get room to be read.