As I mentioned above, I also still carry that big, D-cell light every time I put on a uniform. The benefits it brought to the table 20 years ago still hold true today. Mine is current technology so it is an LED light with a long battery life and excellent candela and lumens. It is rechargeable and rides next to me in the patrol car all shift. When I hop out, it comes along, and if I don't need it I sling it through a ring on my belt.
I love the ability to tuck it under my arm, conduct searches through crime scenes, and even use it as an impact weapon, or "improvised baton" should the need arise. It is bulky, but that bulk has value. Many of the new officers I see fresh out of the academy seem to favor the small, handheld tactical lights because they are easy to use and fit nicely on a belt, but they quickly find their limitations and, after a short time on the job, a bigger light usually shows up in those cops' gear bags, too.
Tactical Lights
Speaking of the small, handheld tactical lights, there are probably more options in this category than all others. These lights hit the law enforcement scene in a big way about 15 years ago when the idea of using flashlights as fighting tools became more mainstream. They're generally very affordable and the newest ones have great lumen ratings.
For close-quarters work like shooting or clearing a building they're awesome. They fit easily on a belt or in a pocket and, if all else fails, they'll always be there in a pinch. Options like end-cap or side body power switches allow you to pick a light that will fit your specific tastes and some offer aggressively machined bezels for use as a defensive weapon. I've got one on my belt and a couple others in my gear bag as backups. I even keep a smaller one clipped inside my vest as a last resort.
Common drawbacks of these lights include the inability to tuck them under an arm during administrative tasks, their general lack of candlepower, and frequent use of disposable batteries for power. We probably all have one of these and I'll bet yours also takes a couple of CR123 lithium batteries to keep it lit. If you're trying to blind an assailant they're great, but if you need to light something up at distance, you might be disappointed.