"Cash out"- question

I've seen this new option, I know what it is but I was scared to try it at first because I wasn't sure on what happens. For example if you had outcome a and b, you laid b at 1.3, it rises to 1.5, if you cash out will it back it at 1.5 or back outcome a at 3s etc? I haven't tried it because I see that most of the time I can cash out more if I do it manually than cash out button but just wondering how it its done.