As you all know a GRID is a collection of nodes. In Informatica we use grids to improve the performance while running sessions and workflows. When you run workflows and sessions across nodes of a grid, it Improves the workload on the Integration service and makes the processing quite faster.
The Distribution of workflows and sessions across nodes is done by the Load Balancer. Grids comes into effect when performance degrades due to memory storage becomes a problem.
Grid will use more resource to run the session and hence will improve the performance. Also while running workflows on a grid Integration Service loads memory and CPU resources on nodes without requiring coordination between the nodes