If you're sailing in a class event where membership in the class is required, you should/are required to use a class sail. If you're in an event with no class membership requirements, you should be able to use less expensive equipment (sails/masts/bailers/ect).
Everyone seems to be quick to recognize Intensity sails as ok replacements for class sails and from what I have read on TLF they don't seem to be any faster or slower than class sails. But, now that I know I don't need to race with a class legal sail, what if I buy a "practice" sail from my local sailmaker for less than an Intensity sail and, oh by the way, the sailmaker tweaks it just a tiny bit so I can point higher, or go just a teeny bit faster? Are you going to say ok to the guy with the Intensity sail and no to me?
And where does it stop? If it is ok to use sails that are not class legal, is it also going to be ok to use afermarket blocks? blades? Spars? ??
You can say "this is all crazy, who would do that for fleet racing?" Well, it does happen, I have raced against some people who thought winning the annual race in the middle of nowhere was the most important regatta on the planet.
It seems to me that the single most underappreciated part of Laser sailing is that fact that we can arrive at a regatta and assume that all the boats are identical and that the racing will be sailor against sailor. Further, a simple glance at a boat reassures you that this must be true (unless someone has spent a ton of money to hide it). But if you start allowing aftermarket equipment during racing, how can you be sure that the guy who won was really the best sailor?
Just my two cents as a sailor and not as a class official.