It is extremely dangerous for both officer and the fleeing rider. Another concern is that with some modern sportbikes, the police simply can't physically catch them. Police cruisers usually end up topping out at 120-140mph due to all the gear they carry, and to make things worse motorcycles don't get held up by other traffic like a fleeing car does. In a wide open run, many of the latest superbikes can even outrun the police helicopter, let alone the cars.
Top speed of cruiser - ~140mph but is slowed by traffic.
Top speed of typical police helicopter - ~161mph, but range is extremely limited at that speed.
Top speed of stock 2000 Suzuki Hayabusa GSX-1300R - 212mph.
Top speed of modified Hayabusa - ~260mph (Yes, faster than a Veyron.)
Which is why many departments don't even bother pursuing a speeding motorcycle unless there's some other reason - such as wanted in a felony, crime against person, etc., etc. If speeding is all, many departments will let them go.
That's not to say that they won't get your license plate and be waiting for you at home instead, though - which is the usual flipside of such a policy.