Gross motor skills involve using your whole body and are absolutely essential for a child's physical and neurological development. Mastering gross motor skills allows children to develop the muscles they require to perform everyday functions (e.g. walking, running, dressing themselves) and also helps them to develop connections between both hemispheres of the brain, as they have to learn to coordinate both sides of the body at the same time.
Whilst kids can follow this video without the lines on the floor, they will likely have more fun and engage with the exercises for longer with the lines. I use masking/painter's tape on the floor inside because it's easy to remove afterwards. You could also take them outside and use chalk to draw up some lines.
This is an activity that will hopefully keep little people engaged for much longer than the length of the video, so let them have fun and make up their own ways to navigate the lines.
I hope you enjoy!