Someone calls me on the phone for a consult. They tell me, "Richard I was pulled over for not using my turn signal. When they asked for my driver's license they said they smelled marijuana. They got me out of the car. They asked if they could search and I said sure. The cop searched and found a crack pipe and some old Xanax. They never found any weed. Now I'm charged with possession of drug paraphernalia and misdemeanor possession of controlled substance. " The next thing they say is "I didn't get a ticket for the failure to use a turn signal.
Also, they didn't find my weed since I smoked it all. Can't we just get it all thrown out? After all, they stop was bogus or I would gotten a ticket. " Just because you don't get a ticket doesn't mean that you walk on the other two charges. The cop has discretion in deciding which charges to file. If he didn't find something else, and you passed the attitude test (I.e. you were polite and didn't act like an idiot), they might have just given you a warning.
The other reason he may not have given you a ticket is that he was concentrating on your charges. If he writes you a ticket, a good lawyer may take up the ticket case first looking for holes in the possession case. Many, not all, municipal prosecutors are less experienced and might not spend as much time preparing the case. They also have more limited interests than prosecutors handling the more serious charges. A good attorney can actually sometimes use the ticket to actually benefit the client.
Cops know this. That's why they might not write the ticket.