BuddyPress.org

What @r-a-y said. It can be nice to use templates if you think that other BP themes will possibly provide override template for what you’re building. Unless you’re building a BP plugin that has extremely rich functionality or can only work if it’s extremely customizable, I wouldn’t worry about it – just put the markup code directly into display(), or in a function that gets referenced in display(), or required as in the Group Wiki plugin.