When you purchase at locally owned businesses rather than nationally owned, more money is kept in the community because locally-owned businesses often purchase from other local businesses, service providers and farms. Purchasing local helps grow other businesses as well as the local tax base.
Local businesses often hire people with more specific product expertise for better customer service. You are also going to see these people around town and they are more likely to serve you better because they have to face you day after day.
There’s a lot of talk about exerting influence with your purchasing choices, or “voting with your wallet.” It’s a fact that businesses respond to their customers but your values and desires are much more influential to your local community business than the large big box stores.