Postable commands are a last resort kinda thing imo… They return void, and take no arguments apart from the command ID and you can’t use them in conjunction with other postable commands. They are simply what all the buttons use to initiate a command. Similar to a Dynamo graphs in this way… they are run, they do what they do and then that’s it.
We typically don’t use these in code because of these limitations, but there are some exceptions where they might be useful, but not that often. I usually try write my own functionality to replicate as much as i can what a postable command really does, but sometimes this can be quite tricky if the parts of the API it uses aren’t exposed. I wrote about here also…
Dynamo Node code you’re looking for will most likely be in the DynamoRevit github so check in the link below…
I hope this helps.
Cheers,
Dan