Most people find your channel when you are not live. A posted schedule is the only useful thing an offline channel can say to them.
What the schedule feature actually does
Twitch's schedule shows on your channel page and lets viewers follow specific slots rather than hoping to catch you. It turns "I liked that stream" into a time they can put in their week.
Consistency beats frequency
Streaming five days a week at unpredictable times is harder to build an audience around than three days at the same times. A viewer cannot form a habit around a schedule they cannot predict.
This is also why a schedule you do not keep is worse than no schedule. It converts "when is she live?" into "she said Tuesday and she was not there."
Pick the days you can actually hold. Channel Check looks for five, but four you keep beats seven you miss.
The honest caveat
We measure whether you have a schedule posted and whether your streams match it. We do not claim that posting a schedule causes growth, because we have not measured that and neither has anyone else who says so confidently. What it does is remove a specific, fixable reason for someone who liked your stream not to return.
More in the Channel Optimization guide.