When a customer purchases or does anything with bitcoins, he/she would have a track of it. All transactions can be monitored at any point. It helps save more money as well. No third party's involvement. If more bitcoins are used, then many merchants would start accepting it. Its very comfortable for them as they no need to go to bank for any other transaction they make. There are many other good reasons why customers use bitcoins.
No taxes for buying something with it as it is not connected to government at all, but only if it is accepted somewhere near you, because we can always see when we go to a market and do some shopping and while paying the bill we get a lot of taxes applied on the things we have bought, we wont face that thing if we are using bitcoins.
If the country in which to live is necessary to submit the declaration of income, then you are not lucky bitcoin.