target container + codecs auto-detected when re-encoding with ffmpeg?

[pxstein]

Assume I (lossless) re-package a video file with original container A into another video container B (e.g. AVI or MKV or MP4)
with an ffmpeg container like

ffmpeg -i myvideo.<sourceextension> -vcodec copy -acodec copy myvideo.<newextension>

Does ffmpeg AUTOMATICALLY recognizes the target container type from the extension of the target file name?
If yes: Why do I sometimes see sample commands with an additional flag like

ffmpeg -i .... -f AVI ....

[Selur]

Does ffmpeg AUTOMATICALLY recognizes the target container type from the extension of the target file name?

normally yes.

If yes: Why do I sometimes see sample commands with an additional flag like

ffmpeg -i .... -f AVI ....

to make sure the auto detection chooses the right container (normally not needed unless you use an extension ffmpeg doesn't know/support for that container type).