I keep wondering about adwords buying for a small SAAS. At $1/click, and then maybe 1%-5% conversion for a paying user, and even if this is a generous 100$ ann

I keep wondering about adwords buying for a small SAAS. At $1/click, and then maybe 1%-5% conversion for a paying user, and even if this is a generous 100$ annual subscription .. its just terrible. Does this really work long term ? (disclosure : i worked in a big B2C that spent 8 digit sums on incoming traffic so obviously it works..)