Room to read.
A good reading space begins with a little room. The margin gives the eye somewhere to rest. The line gathers a thought, carries it forward and lets it land.
Change the controls and watch this paragraph move. A larger letter does more than occupy space. It changes the number of words on a line, the height of the passage and the rhythm of every return.
Typography is a sequence of choices you can see.
Build the page for the words it holds. Then test it at the size where people will actually read it.