Apart from impulse shopping, we all plan what we buy. If a product comes with a return policy or a warranty, you may want to plan for contingencies. Companies expect returns to be rare, even when you aren't happy. Some common sense and a little preparation will make life much easier if you decide to be the exception.
A friend of mine buys things with the expectation that many will be returned. This allows her to check products at home to see id they fit her vision. Once she has decided, she spends an evening of unshopping to return things. This seems excessive to me, but returns are much easier if you do a little planning.
Start by filing all the paperwork -- warranty, refund policy, instructions and especially the receipt. I create a separate folder for each item to keep warranty and instructions. I keep a separate folder for each store where I purchase things to hold receipts. If a product comes with a 30 day return policy, I leave a note about it on my calendar for a week before the return privilege expires. Any phone numbers, addresses, email addresses or other information I need stays with the receipt.
Another case where you may want to track dates is scheduled maintenance. Cars are the most obvious but not the only place where this applies. A calendar or tickler file will help you meet your end of a support agreement so you can make sure the manufacturer does too.
If the product fails, you can go to the product information folder to examine your warranty options. This information is kept by product because it isn't time sensitive. When the product fails, it has either outlived its warranty or it hasn't.
Finally, should you buy an extended warranty or not? An extended warranty is essentially a form of insurance, and it is offered because the offerer expects to profit by it. My rule is simple. Accept and negotiate for any warranty that is free. Don't buy an extended warranty if you can afford to replace or be without the product. If you want to see the effect, create a savings account where you pay yourself the warranty price and withdraw from it to replace failed products.
Many products come with return policies and warranties. With a little tracking and preparation, you can be in a much better position when shopping becomes unshopping or a warranty needs to be honored.