Why is it that if you select new it adds more money, is that because of the bonus depreciation

Just to confirm, If I bought a Used boat for my fishing business, I select "I Purchased this asset new" - Is this correct? There are many different answers from...

If my profit was only 25K but my fishing boat was 55k, can I use 179 for up to 25k plus the 50% depreciation or just the 25k?