Technically, w/o engaging the autopilot, you don't! But have you ever tried to apply a crab angle when the CDI is 90 degrees off. You have, say, the CDI set at 090 on an ILS to runway 18. It will work fine except try making a 3 degree correction while looking at the CDI off 90 degrees.
This is not so for coupled approaches, the A/P needs to know the course.
GF