What do you mean, like if you used a visa card to pay for something using your own fiat, but the transaction was done through blockchain?

honestly, I don't see any advantage to this.
As it stands, electronic fiat payments are all pretty open, you can easily check and track your money and purchases anytime.
There is no problem at all with people tampering with it and many safety guards in place if someone does an unauthorized transaction.

Using blockchain as it stands now, however, has a lot of drawbacks.
First off, the cost is very high now due to the lack of scalable technology.
There are projects like nano and iota which could work if mass adopted.
Also, confirmation times don't scale either.

blockchain has way better uses than for just simple everyday small purchases.