A game mechanic is something you are going to make your players do. Think of it as some kind of system, and you're trying to nut out how it should work, hold together, look from their perspective. Whether to have on-map battles or encounters, how a crafting system should work, etc. Also, it's for discussion of ideas about these things - what could/should be included and what are the implications. When it comes to actually implementing it, that would go into the Support or Script/Plugin forum for the particular engine. Game Mechanics Discussion is purely theoretical.
Your question is a general "what's your preference" type of thing. It's got nothing to do with mechanics - how your game works under the covers, what the player gets to do.
There is no "Project Discussion" forum, so I'm not sure what you mean there.