The benefits of calculating winnings are:
To work out the potential winnings before placing a bet. You can place your bet knowing your possible returns.
To work out actual winnings after the completion of a bet so they know what to expect back.
The first means you can make a decision about if a particular sports bet is worth the potential outlay and the second is so you can work out the winnings. As well as doing the hard work our free versions also take into consideration Rule 4 deductions and any dead heat races.