Hold on a second. Yes, free play is converted to cash for the play in video poker, but you don't get to cash it out.
Example A
You have $5 of free play and bet 5 credits. You get a pair of jacks that pays $5. You cash out the $5. There is no more free play for you to use. The $5 of free play was converted to $5 of "coin in" and your $5 of coin in hit a break-even bet.
Example B
You have $5 of free play and bet 5 credits. You get three of a kind that pays $15. You cash out the $15. There is no more free play for you to use. The $5 of free play was converted to $5 of "coin in" and your $5 of coin in hit a three of a kind.
Example C
You have $10 of free play and bet 5 credits. You get a pair of Jacks paying $5. You cash out the $5. There is still $5 of free play remaining for you to bet as free play -- but it is not money you can cash out in video poker.