Download score based load balancing
With download score based load balancing, GTM estimates the load on your data centers based on how long they take to respond to GTM liveness tests. The advantage is that you do not need to implement a load object. The disadvantage is that this is a very crude measure of load, and usually highly nonlinear.
As load increases, download times do not increase significantly, until there is too much load. When that happens, the download times skyrocket. This can easily cause erratic load balancing or load oscillations.