I would consider myself a medium-level player (APA 5) and don't know much about racking or breaking.
Conventional wisdom where I play is that if you have a really tight rack, you're more likely to get good spread with the same strength break.
But in my personal experience, I have noticed the opposite. A really tight rank tends to give me worse/"dead" breaks, and a rack that's a bit loose is more likely to explode.
I've told this to people but most people think I'm crazy for thinking this.
A friend of mine and I did an experiment a few months ago where we would rack really tight, a bit loose, and extremely loose, break, and see what happened. It wasn't very scientific since we could see how loose the rack was, but how loose the rack was didn't seem to make a noticeable difference re: where the balls ended up on the table.
I haven't thought about it very much from a physics standpoint but it makes some sense to me to look at it this way: with a tight rack, the balls in the front/middle don't really have anywhere to go other than to transfer energy to the balls behind them more efficiently. So the balls in the back get more of the energy. This is fine if they happen to bounce around and hit the other balls again. But if they don't, you end up with a clump of dead balls near where the rack was.
Of course a more skilled player might have a very particular goal when he's breaking (e.g., make a particular ball) and that means he has to have a consistent, tight rack. But if you're just going for a nice spread, I'm not convinced that the tightness of the rack matters much.