Concurrent capacities allows the reduction of time in scheduling, so if you have an operation taking 60 minutes but a concurrent factor of 4 the time scheduled is 15 minuttes.
Efficiency relates to the time again - how efficient is the work centre? If it is 75% efficient then a job taking 60 minutes will actually need 75 minutes to complete due to the inefficiencies
This maybe an old post but I have a similar question but related to costing. We have set the concurrent capacity to shorten the production lead time. Is this affecting the standard cost calculation of the item?