While most people aren’t going to realize that you are using a theme that someone else made for your WordPress site, it is the first thing they will see when they open your page. Taking the extra time to choose a theme that will enhance your site rather than take away from it will benefit you in the long run. Free themes can be very appealing, but depending on your site, you may need to look at a premium theme. Premium themes may have more features that you are looking for. Definitely make sure that your work is exactly how you want it to appear before publishing it live. Maybe even ask coworkers or friends to view it before going live.