From my understanding, you can set the values of a table to be weak with like this:

local x = {}
local m = {__mode = "v"}
setmetatable(x, m)

You can also set the keys to be weak with __mode = "k" and both the keys and values with __mode = "kv".

So my question is this:

What are weak tables useful for? Will I find myself using them in the future? Could I use them to help prevent possible garbage collection issues?