I tried lead conversion in latest version demo,
I found that if you are converting lead, account and contacts are auto created and for opportunity it is required to enter opportunity name and expected close date.
But if you enter the details and do not click the create opportunity button and directly click save and convert button then it will not create a opportunity and it will not allow you to do that again, no convert option is available anymore.
I suggest if those details are filled up and if user clicks on save and convert button it should at least give alert to please create opportunity first,
or auto create opportunity if details are filled up and user have clicked save and convert button.
This will avoid the confusion.
Another thing I found is If you have entered likely, best and worst values in opportunity as 700, 900, 500 respectively and if you change sales stage to closed won all the values are saved as likely value.
Is it set like that only or its a bug?