Stucco is a rigid material on a house that moves. Settling, temperature swings, and the occasional earthquake all leave marks, so almost every stucco home in Los Angeles and Ventura counties has some cracking.
Hairline cracks, thinner than a credit card, are usually cosmetic. They should still be filled before painting, because even small cracks can let water behind the surface over time, and they'll show through fresh paint.
Wider cracks, cracks with edges at different heights, and diagonal cracks running from the corners of windows and doors deserve a closer look. They can point to movement in the framing or foundation. When a crack goes beyond a surface repair, we'll tell you so, and suggest having it checked by a structural engineer before we patch it.
For most repairs, the fix is to open the crack slightly, fill it with a flexible patching material or new stucco, and match the texture so it blends in. A quality exterior coating over the repair seals it and makes the patch disappear.