A good set of custom floor mats keeps salt, slush, and mud off your car's carpets, saving you from a nasty detailing bill come spring. These heavy-duty liners usually run around $250, and prices tend to spike right as the first cold snap hits.
Timing your buy for late autumn before the weather turns bad helps you beat the rush. We can spread out that cost so you are not taking a hit all at once.
The intro window is a deadline, not free money. If you still have a balance left when the 18 months are up, interest kicks in on the original amount from day one, which wipes out the whole point of spreading out the payments.