Breaking down a process or system into smaller modules to make it more accessible/easier to comprehend.
On the other hand, it also mean over-complicating a simple process to the extent of being anal in the extreme.
Normal Bloke: Here you are Old Lady, let me help you across the road.
Old Lay: Thank you, young man!
Project manager: Now then Normal Bloke, we need more granularity here. Firstly, what road are you referring to? Next, is there any traffic on said road and if so, at what speed is it travelling? We also need to define the camber of the edges and the traction factor of the tarmac under the temperature of the day to ascertain the breaking distance of the road users in case of a Normal-Bloke-Old-Lady-slippage scenario. Next, we need...
Normal bloke: Fuck this, I'm off to Macdonalds.