This is, of course, probably only my opinion. But I think starting way faster than your goal pace is extremely idiotic, just from common sense, but maybe that's just me. So I would personally recommend being familiar with your goal pace and trying to run consistent splits. I mean, it's ok if you start out for like, 30-60 seconds at a pace significantly faster than your goal, and so it's OK in my opinion to have a first mile a bit faster than goal pace, but if your goal pace is 5:48 (18:00), in my opinion it is dumb to be any faster than 5:40 for any mile, unless it's the last mile and you felt really good.
Here's another way of looking at it: some people consider this to not be "real" racing, but isn't it just so much more fun to actually feel like you have stuff left in the tank for the last mile? Maybe some extremely in-shape people whose minds work differently are physically able to start out well under goal pace and still maintain goal pace for the final 2 miles, but otherwise, I really believe racing is SO much more fun when you space out your moves so that you are able to speed up as the race goes along, and that way you will pass a lot of people. :) To clarify, I'm not advocating having anything left in the tank at the end - just having enough left with a mile to go that you're not absolutely dying and getting passed by a bunch of smarter racers. Then again some people might love that feeling of dying for 2/3 of a 5k race. I guess we're all different.