Angular resolution
A laser beam is millimetres wide; a radar beam is metres to kilometres wide. The laser lights one spot on a target and gives a pinpoint range. The radar lights a volume and gives an average range. For shooting, you want the laser. For finding, you want the radar.
Range and weather
Radio waves shrug off clouds, rain and dust. Lasers struggle: dense fog or heavy rain cuts range by an order of magnitude. A radar that works at 200 km in clear air still works at 150 km in monsoon. A laser that works at 10 km in clear air may not work at 1 km in fog.
Stealth
A laser beam is invisible and narrow — only a target with a laser warning receiver pointed at the source detects it. A radar broadcasts widely and can be detected at twice its own detection range by any RWR. Laser rangefinders dominate close-in targeting precisely because they don't give the target a chance to react.
Combined systems
A modern tank or attack helicopter has both. The radar (or millimetric-wave seeker) finds and tracks at long range. The laser fires once for ranging just before weapon release, optimising the firing solution without long laser exposure. The same principle applies in autonomous cars: long-range radar for situational awareness, LIDAR for the final geometry.