I have to admit that Scottish court procedure is not my strong point!
Here is a link to the process of appearing in a Scottish court.
Report of the Summary Justice Review Committee
www2.gov.scot
The only thing I can think that differentiates between if you appear on the court roll or not is that court roll business is like the English summons system where paperwork is served on you by post at a later date, whereas if you are charged and bailed directly to court then it does not appear on the court roll as it is police direct case. (Note that I am using English court terminology not the Scottish ones which are different)