that feature has been there for at least 6 years (for as long as i've been working with SF). It's the most basic relationship using a custom object.

Yeah .. only real downsides are above: * You have a certain number of Custom Objects you can use which cost $X * There's a maximum total you can have (not to be exceeded) * It's another thing to watch / maintain / document * The land of custom objects and fields can get polluted so .. hopefully you have decent governance in place.