It is not so easy to find information on forums about possible settings that can be set with app_config.xml.
How about opening a specific thread about it. (or have I missed some?)
For example I have following question.
Do primegrid GPU applications support settings like <gpu_usage>.4</gpu_usage> or <ngpus>.4</ngpus>? Which ones do?
I've tried to use them and had no success.
Could you please collect description of all possible settings for all applications in one thread or at least one for each application in relevant subfofums.