There seem to be some misconceptions to what purposes the array can serve. I'll add to some of that confusion with my own experiences.
DethAdder's use of the array to boost movement is a prime example of one of the more practical uses of the array. I don't use it to its fullest benefit, but park my transports and attack ships at the edge of the array, closest to my intended target. In many circumstances, it's advantageous to start and end a war in the same turn. I've found that a very effective way of doing that is to completely exterminate the enemy in that one turn. The array can boost your speed quite nicely for that purpose. The ships need to be parked under the array's influence for one turn before they'll get the speed bonus.
Prior to the attacks, I like to trap some enemy fleets within the array's influence. Usually, this is also on the edge of the array, so the maximum benefit isn't used. Most times, it isn't needed. A fleet of constructors or tiny fighters can surround the enemy fleet and they wont move until war is declared. If I have enough ships, I make corridors so the enemy fleets can move closer in or let incomplete fleets join together. That makes them easier to destroy once it's time to do that. This tactic can be useful when it becomes clear that you can't wipe out the enemy in a single turn. The AI appears to consider the loss of its military strength compared to mine in that turn and will sometimes surrender, thus ending the war.
Another use for the array is that early on, it acts as a lure. It actually attracts enemy fleets toward it so they can be trapped. The fleets are usually frigates, but the AI will continuously upgrade them and spend BCs on an eventual lost cause. Fleet maintenance costs help keep the AI's budget slowly draining off so I don't have to do as much to match them. It's real nice when a fleet of battleships comes along for the snare, too.
The diplomacy bonus of a strong military rating is nice, but be aware that the first few ships parked under a beginning array can backfire. Depending on your strength beforehand, the little ships can actually lower your military rating. Like everything else, there's a balance and timing involved.
There are too many nuances to list, but the idea here is to resist painting something with such a broad stroke. That being said, the array can boost scores very high and in the latter part of the game, that becomes its final purpose.