Smart beaconing, as compared to fixed time interval, increase the effectiveness of both the RF spectrum and detail plotting on the map. Smart beaconing combines change of course (heading) with speed and thus also induces a randomness to the packet transmit time. Most APRS beacons are not polite, the just blurt out the position when needed. There is a way to sequence the beacons based on GPS timing, but for most purposes, smart beacon creates the same randomization. 

The Byonics, WX3in1 and Argent TNC in the DR135 radio all employs Smart Beacon.

From a practical standpoint, we are always interested when the tracked object “turns the corner” so Smart Beacon is the key!

A lot more information is available at this website

The below picture shows some tracks are diagonal across intersections (corners) and is thus not s smart beacon, while another defines the block by beaconing on heading/course change.