Let me add few comments regarding mentioned subjects:
Altium doesn't support courtyard directly
Yes, and this is significant fault of Altium- it does recognize courtyard as the entire footprint, means it allows overlap when rules covering gap between components are set to 0. You can compare it with Allegro, where â€œPlacement Boundaryâ€ layer is courtyard layer- take a look at pic from attachment: if one try to overlap those boundaries that will give an error, however courtyard edge overlaps are allowed- which is correct and logical obviously. So Altium sucks here
Assembly houses don't normally need the courtyard information for the assembly process - the courtyard just helps you to create a design which could be assembled without problems.
Correct, it's not required for assembly completely, you only need it at design stage.
I personally prefer using a separate layer for the courtyard as it gives me more flexibility and the ability to do whatever I want with the silk screen. I also use the courtyard layer for assembly drawings.
If you mean duplicating courtyard geometry also on silkscreen layer that generally is only possible when you use N and M pattern density according to IPC-7351, while in case of L you most probably will not be able to make such contour without violating â€œSilk-to-Copper distanceâ€-like rules.
Meaning the exact requirement in courtyard definition: biggest benefit of it is possibility to achieve most dense placement while still remaining with IPC-7351, but it's obvious fact that far not all boards require that kind of placement. I'll tell you more, lot and lot of board are physically just oversized(artificially) to perform fast and easy component placement using grid- it's standard and mainstream approach, but it doesn't work in true high density designs. At the same time, placing components courtyard edge-to-edge in 90% of cases will lead you to high-end HDI designs area, but it's not main case: such placement isn't based on grid but on geometrical transformations thus being most complicated and time consuming method- however bringing the most high quality result by all means. If one doesn't have experience in such placement it's very easy to mess with your project in such way that will definitely turn into deep relayout/redesign