One of the misconceptions of the idea of a full-time employee is that they have greater commitment than those who work a semi-regular work schedule. From my own experience as a part-time employee, as well as from witnessing the work of my colleagues who work second jobs, the commitment level I have seen often is far greater by those who work less than 30 hours a week in a position.
In terms of reliability, people often associate someone who works 5 8 hour days as someone who is committed to a company. However, from working with SAHMs (stay at home moms), virtual interns, and freelance project managers, I have seen the same type of commitment (if not more) in a 5-10 hour commitment to work than from people who work a traditional workweek.
People with kids, other jobs, and other commitments have other “full-time” commitments that require complimentary “part-time” commitments. The work they do often is a mental escape or a mental boost to help them break up their week and expand their range of influence. As well, they give 100% knowing that they only have 1-3 chances a week to see you in person and want to put forward their best effort.
The next time you are considering expanding your staff, consider opening up some roles for people who can only commit to a few days a week (or a few hours a day) and train them on a specific set of roles and responsibilities. Similarly, consider giving people who have been committed to you full-time to stay on seasonally or part-time to keep them involved in your business.