All work matters because all sides to the work done gain from the work. Participants learn new skills, meet new contacts, and help get things done that may not have gotten done without volunteers helping.
It is usually unknown who exactly will be showing up to volunteer on a project and those doing the work also often meet new people from a variety of life backgrounds. The connections you make with coworkers, suppliers, recipients, and organizations can make a difference to you long after the work is done.
When you know you have made a difference you feel better about yourself. It is important to take pride in your volunteer work and do your best work.
Those receiving the benefit of the work done are lifted up improving their own lives. Volunteering, working side by side with others, connects you to other human beings. When you volunteer, you are making connections. Paid for your time or not, always do you best in your work. It matters.