One of the chief benefits of substitute teaching is that you are free to create your own schedule. While school districts generally have some minimum requirements that you must work each month to stay active in their system (check with your current school district to find out what applies to you), generally you can pick the times, days, or even schools where you would prefer to sub. This is invaluable if you have frequent scheduling conflicts. For example, perhaps you take a relative to the doctor on a regular basis and always need a certain day off every so often. Or maybe you are the "go to" person in your family. Perhaps when one of the grandchildren are sick, your son or daughter call on your to babysit, so they don't have to lose a day at work. There are many scenarios of why you might need a day, or half-day, off. With substitute teaching, it is as simple as either taking the job or not taking the job. It is up to you.
Not only can you take full days off if needed, you can also take half-days off. Perhaps you need to go to the dentist in the morning, but have your afternoon free. You can grab a half-day job, it is yours for the taking. This kind of scheduling freedom relieves you of the tension of mentally doing gymnastics trying to arrange people, places, and events so it all works out. Think about when there is inclement weather. If there is a lot of rain, snow, or ice and you are concerned about travel ling safely to work, no problem. Just don't take a job that day.
Substituting allows you to work and make money on your terms, no longer bound by a daily schedule that simply won't work easily in your particular life.