This isn't necessarily a stroke of genius but it's a goo thing nonetheless. When I bought this house two years back I was single and hadn't discovered mustachianism yet. Hence my mortgage came with a PMI of $177/mo. Now, I am married to a beautiful mustachian woman and our finances are in a good place.
Putting this amount of money into my principal will not only save us the $177/mo from PMI (which we wil direct back into principal) but will also bring us to the point where we'll be paying an extra $100/mo in principal (or less interest, however you want to think of it.)
Leading to a grand total of $277/mo more towards our stache.