I'm fairly new to RenPy but from my understanding:
The first option is quick and dirty. If you want to just generically play a Fullscreen video with minimal options, this will get it done.
The second option gives you more control over the video as well as what's going on in the scene at that time.
Sidenote - once you've declared your image you don't have to call the movie file. Instead of
play movie "video/On_Your_Mark.webm"
you can just do
scene yourmark for the video as a new scene or
show yourmark to overlay it.
One "pro" for option 2 is the ability to continue dialogue during the video. For example...
This will play the video and then display mc's dialogue once the video is over and control is returned to the original scene:
Code:
$ renpy.movie_cutscene("On_Your_Mark.webm")
mc "Hey, I'm talking here!"
This will start to play the video and immediately overlay mc's dialogue on top while the video is still playing.
Code:
image yourmark = Movie(size=(1920, 1080), channel="movie_dp", play="images/On_Your_Mark.webm")
show yourmark
mc "Hey, I'm talking here!"