If you have the space in your main panel for a dedicated circuit or circuits and don't have a very long or excessively complicated run, what is the logic for a sub panel?.
As MC pointed out, it's just extra stuff
True. If you have space on the main panel, wire the dedicated line on one leg and move the high-current devices and appliances to the other leg. It's been recommended to install these appliances as far as possible from the audio line on the panel.
I know, I know, these circuits are shared in the panel and not isolated, but there may be a benefit of less noise from appliances like a/c or furnace switching on and off.