There is no requirement to apply for a trademark prior to using it. Trademark rights in the U.S. are granted to the first one who uses a mark in commerce on particular goods or services, not to those who are first to file with the exception of Intent-To-Use applications that ultimately mature into registrations. If you’re not trying to stay under the radar, then the potential benefits of filing a trademark application outweigh the benefits and risks of not applying, provided you have a competent trademark registrability search conducted before you file.
If you’re concerned about building and protecting a brand in the long-term, why limit your business to merely common law rights? It will cost you much more time and money to defend a trademark infringement lawsuit by proving you had priority (earlier) of use of your common law trademark than if you had simply registered your mark.