When downscaling meteorological data by using limited area models, many support forums recommended you to downscale incrementally in small steps. For example let's assume that your input data is on a 27x27 km resolution and you need data on 1x1 km resolution.
A suitable setup would be to downscale in three steps, incrementally increasing the resolution: 27 km -> 9 km -> 3 km -> 1 km
Why should I not simply use the following set-up? 27 km -> 1 km
The main motivations I've seen for this is that the intermediate domains (9 & 3 in the example) won't require that much computational resources compared to the final domain (1 km). But that can't be the only reason.