It's basically used to achieve steady state blood levels sooner. Normally it would take 4-5 half-lives to reach steady state, but by using a loading dose you are able to reach a plasma concentration of the drug which falls in the therapeutic window (yeah, define this range with AAS!) after only one or very few doses over a short interval (1-2 weeks). The dose is larger than the dose needed to maintain blood levels in this range (again this range is not well defined for AAS). So you use it to reach consistent (steady state) blood levels sooner (as opposed to not using a load it takes 4-5 half-lives to reach steady state, which is why you don't see the dramatic effects with test enanthate or longer esters until the 4th week or so with conventional dosing----the half live is approximately 6-7 days, so 4-5 half lives of test E is around 4-5 weeks. So like Zygla said, since you reach steady state sooner, you could use this method to decrease length of cycles because you are at therapeutic levels sooner, and can omit the weeks it takes waiting to get there.