Most homes in Manatee and Sarasota counties are concrete block covered in a thin coat of stucco. As the house settles and the walls heat up in the afternoon and cool at night, that stucco moves, and it cracks. Hairline cracks around windows, doors, and corners are normal. They're also an open path for rain.
Water that gets behind stucco doesn't dry quickly. It can lift paint from behind, cause bubbling and peeling, and over time stain or damage what's under it. Painting over a crack seals it for a season at best; the crack opens again and the new paint splits along the same line.
On our exterior jobs we mark every crack first, so you can see the scope. Then each crack is routed open, filled with a flexible elastomeric patch that can move with the wall, and textured to blend in with the surrounding stucco. After primer and two finish coats, the repairs disappear.
Wide cracks, cracks that run diagonally from a corner, or cracks that keep growing can point to a structural issue. If we see one of those, we'll tell you and recommend having it looked at before we paint over it.