It is recommended that you set up sufficient blocks to reflect your farm system management regime and the soil types / topography on which you farm. They should be "management blocks" not small sub areas.
Refer to The Blocks Overview article for further guidance.
You should avoid "over-blocking" - the Simplify tool is available to help you to check if you have made more blocks than the model actually requires to model the farm system you are entering.
If too many small blocks are created the model can struggle to balance feed requirements across the farm and so not provide a reliable result or in some cases provide a feed allocation error. The Overseer model is trying to analyse the effect of larger system changes, not small changes to animal locations.