Complex sentence: Regional models (also known as "limited-area" models, or LAMs) allow for the use of finer grid spacing than global models because the available computational resources are focused on a specific area instead of being spread over the globe.
Split into simpler sentences: Regional models (also known as "limited-area" models, or LAMs) allow for the use of finer grid spacing than global models. Essentially, the available computational resources are focused on a specific area instead of being spread over the globe.