It's because `Amount` is a class in `steem-python` that splits a string like "10 SBD" into `amount`(10) and `asset` (SBD) as you can see [here](https://github.com/steemit/steem-python/blob/master/steem/amount.py).  The `float()` function just converts a number or a string into a float! If you really wanted you could do `recent_claims = float(reward_fund["reward_balance"].split()[0])` instead, but it's easier to just use `Amount` class.