The most common form of piracy by far. Most users don't intend on stealing - they just don't really care about your license terms. Adding hardware locking to your license can reduce casual sharing and multiple installs by innocent users.
Corporate and office workers will just install on any machine they see fit and share with anyone in the office. Most companies don't have a way to track and enforce license compliance so using hardware locking can help eliminate this inter-office sharing.
If its worth buying - its worth stealing. You may have resolved to just accept this theft as inevitable. It's not. A hardware locked license in combination with code encryption and tamper prevention can effectively eliminate pirated use of your software.