A few weeks ago I learned how to borrow money Interest Free from my bank because of how their system works. I also took advantage of that system and another slow system to prolong the interest free period.
First, the bank that I use allows checks to be scanned in from home and deposited into an account. Typically this isn't really that big of a deal, but my bank allows that money to be used instantly, up to $5000 in deposits can be made per day at my bank from home.
So what I did was took a Convenience Check (slow processing time) from another bank, wrote it for the max, and scanned it in. This gave me access to $5000 dollars instantly. Because the convenience check process is so slow, this transaction didn't even show pending until 5 days later and then cleared finally after the 7th day. I checked out the numbers, and I got 5 days of interest free money from my bank because of how their system works.
The convenience check came with a 3% or $90 maximum transaction fee and a 1.99% APR. I think there may be a lot of things you could do with $5000 in 5 days to makeup for the $90 transaction fee and then some; that's only a 1.8% return you'd have to get in 5 days. I've setup stock portfolios that have averaged 1.5% return daily. It is possible just for me that I could have earned 300 or more dollars from this grace period and came out $210 or more positive with this free money. Then I could have paid the $5090 back to the bank and kept the extra.
There's probably a lot better investments one could think of or use this money for.
Improving Your Credit Score
Another advantage I saw in this that could possibly work is to improve your credit score. Technically if the physical bank location is in your area you could borrow money from that bank through convenience check and pay them or another bank before they even know that you just borrowed money to pay them with (paying your credit card at a physical location is oftentimes credited to your account that same day). This would show your credit card balances less or non-existent for almost the entire 5 day period. You could figure out when your bank reports to the credit bureaus (usually around statement due date) and make all of your credit card debt disappear so that they report a lesser or 0 balance. This would improve your credit score until the next report date and allow you to qualify for loans or credit lines you may not have been able to qualify for.
My wife has an account at this same bank so I can run $10,000 through each day. If I did that 3 days in a row and timed it right I could potentially make $30,000 of debt disappear from a credit card for a few days during the report period. I've not done this, but I can see how it may be possible.
"The sky is the limit, until you purchase the Universe" - Thomas Van