When you refinance to a lower rate, that reduces the size of your mortgage interest deduction, which affects your savings from refinancing. The Mortgage Refinance Calculator can take that into account, which is why it asks for your income tax rate.
Look up yo in Wiktionary, the free dictionary. Yo is an English slang interjection, commonly associated with American English. It was popularized after being used commonly by the Italian-American community in Philadelphia, Pennsylvania since the 1940s.
but yo-yo it's also a toy (I think in English it's called the same) so, someone that is a yo-yo can mean that it is a person that can be easily manipulated like a yo-yo or a person that changes humor or personality or ideas, very frequently. Also can be referd as a person, that comes and goes, easily (like in and out of relationships)