If you are You Tube creator then you must be careful before you delete all youtube videos. There is nothing problem on deleting some unwanted videos but deleting all the videos if your channel is monetized is the bad thing.
Here are some reason why you should not delete all videos from you tube at once:
1. Page views decreases
If you delete particular or all videos from your channel, then your page views also decreases.
2. Watch time lowers:
If your channel has no videos then the watch time also falls. So donot delete all videos at once.
What happens next?
If your channel was previously monetized and connected to adsense then deleting all videos may lose your monetization due to less watch time ( less than 4000 hours)
3. Subscribers loss:
Your subscribers may start to unsubscribe your channel or also report your channel when they didnot find any videos on your channel. So never delete all videos at once.
What can you do to change your content of videos?
If your channel is sports type and you wish to change your channel to entertainment type, then you should slowly upload one entertainment videos and delete one sport related videos rather than deleting all your videos. There is no chance of channel demonetization if you maintain subscribers and watch time criteria of your youtube channel for last 365 days.