Why would the prez be given the power to pardon anyone? They were charged and convicted of CRIMES for goodness sake. What is the upside?

Ol' Barack went pardon-crazy. Where was your umbrage then?

Clinton pardoned almost-- 500 
Obama almost-- 2,000
Bush--200.
Trump just 1. 
Just to keep this in perspective.  

It's in the Constitution and was intended to allow the President to pardon groups of people to prevent a national crisis and only applies to Federal crimes. Confederate soldiers were pardoned following the Civil war.  Jimmy Carter pardoned draft dodgers at the end of war in Viet Nam. These pardons restore the civil rights of those pardoned. It has evolved into more than the original framers of the Constitution intended. Presidents routinely pardon the Thanksgiving turkey. Many times the act of pardoning someone will have political consequences, such as when Ford pardoned Nixon, because the pardon can look like the President is giving the pardon in exchange for something in return.