“Read your writing aloud” is a fairly common bit of advice to new (and not-so-new) writers. Reading out loud is supposed to help the writer spot problems with sentence flow, dropped words, and a host of other issues.
It does work, and work well… up to a point.
Y’see, when they’re your own words, you already know how you intended the sentences to flow; you already know how you imagine the characters speaking. You add emphasis where you know you want emphasis, and you pause where you want a pause, even if those things aren’t shown in the marks on the page. You read the words aloud the way you hear them in your own head, not the way they’re actually written.
Reading aloud doesn’t do much for catching punctuation errors, and (obviously) it doesn’t do much for catching homophone glitches. Aloud sounds the same as allowed, after all.
Just like using a spelling/grammar check program, reading aloud will help with self-editing, but don’t rely on it entirely.