To DEPEND on indirect dependencies or not to DEPEND

Hi ports@!

Most probably the question was discussed a lot of times, but I have not found a definitive answer.

If an app depends on libfoo that depends on libbar:
app -> libfoo -> libbar
Should the port of app add LIB_DEPENDS only on libfoo or on both libfoo and libbar?

Simple example (outdated, but the first thing you see in Porter's Handbook): games/oneko is linked with the command

cc -o oneko -L/usr/local/lib oneko.o -lXext -lX11 -lm -Wl,-rpath,/usr/local/lib

suggesting direct dependencies libXext and libX11. However, ldd oneko gives

libXext.so.6
libX11.so.6
libm.so.5
libc.so.7
libxcb.so.1
libthr.so.3
libsys.so.7
libXau.so.6
libXdmcp.so.6

Of course, libXau, libXdmcp, and libxcb are coming from libX11. The port

USES= imake xorg

Additionally, should it just depend on direct dependencies

USE_XORG= x11 xext

or the full dependency list?

USE_XORG= x11 xau xcb xdmcp xext

More complicated example: cad/freecad depends on cad/opencascade that depends on multimedia/ffmpeg4 with default options (can be switched off).

Should freecad port LIB_DEPENDS on ffmpeg4, as it is now, or should it track opencascade options, or should it not depend on ffmpeg4 at all?

Thank you in advance,
Alexey