Running snakemake with multiple conda environments without rebuilding environments every time
Each YAML file will always create its own environment. The packages in each aren't downloaded and installed each time, if they're already installed elsewhere they're just hard-linked in. You'll want to use both --use-conda and --conda-prefix. The latter will point to the base directory in which all conda environments will be stored. This has the benefit that running the same workflow in different places won't result in a new env being created (by default snakemake will do so inside a .snakemake directory otherwise).