What is break used for?

break causes any loop (repeat, for, while) to stop; execution immediately skips to the point after the loop.

This is convenient when you know you are done working half way through a loop. It can also be used to increase efficiency to avoid computing extra, unnecessary later iterations.

Several examples on the wiki with break

Here's a simple example:

Find the first triangular number after 1000:

local sum = 0;
for i = 1,1000 do
	sum = sum + i;
	if sum > 1000 then
		break;
	end
end
print(sum);
-- 1035

Without the break, it would have kept computing up until the 1000th iteration. At that point, sum would have been 500,500, which isn't what we're looking for. Since we're using this for loop, there isn't really a straightforward way to figure out when the loop should stop without using break.