If you reduce the time a role can work on a stage, Synergy will create another (or more!) rows that show you the effort required to get the work done in the amount of time you require. This does not apply when you have allocated a staff member - because you can't clone people.... yet.
If you shrink the timeframe a role type is scheduled to work on a project, whereby the role becomes overallocated, the row will split into multiple rows. When you try and adjust the duration, the multiple rows will be treated as one timeframe, until such a time, that it can be completed by one resource.
When a new bar appears, the first bar will be allocated at 100% and the other bar(s) will be allocated the remainder.