It's admirable that they want to find real crooks, fight real crime, and keep the city safe from hardcore thugs. However, they often fail to realize that much of police work is found in the little things, which you so often stumble upon during random patrol.
It's not fair if you overspecialize in one area and leave everything else for other officers.
There are two more concerning variations of officers who are out of service, and not just with specialized arrests: the "I'm in training, volunteering at a school, at a leadership class, etc." cop and the "I'm taking yet another sick day, a vacation day, a mental health day" cop. The first officer is often trying to get promoted, so he or she will either take or teach every class, attend every conference, and volunteer for every school, on subjects ranging from schizophrenia to dandruff, all in an effort to pad the ol' resumé prior to the testing process. Again, admirable and good for them, except when it hurts the personnel staffing for those days or weeks.
And the officer who seems to be gone all of the time due to sickness, vacation, or constant schedule manipulation (wanting to come in late or leave before the end of shift) may have other issues besides just running out of hours. These are often the signs of job burnout, depression or PTSD, home problems, or end-of-career blues. Supervisors for these officers should be empathetic and ready to provide resources, but firm about the impact on our business of keeping people safe, even when you don't always feel like working.
None of this is to say that being a dope cop, a candidate for MADD's yearly drunk driving arrest award, an auto theft car and suspect magnet, or a felonies-only cop is such a bad thing, only that it violates one of life's important principles: Your strength, taken to an extreme, becomes a weakness. Focusing too much on one type of crime or crook hurts your partners, your squad, and even your agency by taking you out of service too long. In these days of perpetual minimum staffing, there are plenty of radio calls to go around. Share the wealth.