Sometimes the largest cases start by investigating the smallest incidents. I remember hearing stories in the police academy about how large drug rings were cracked or large fencing rings discovered just because an officer decided to investigate a simple broken brake light or failure to use a turn signal. Even if investigating a small case doesn't lead to cracking a large case, the paperwork trail can be useful for solving subsequent cases. The “Son of Sam” case, where a serial killer was terrorizing New York back in 1976, was eventually solved because a parking ticket near the scene of one of the crimes led to a license plate. This led to a suspect, and David Berkowitz was eventually convicted of the crimes.