Localhost folder size

Plex Media Server
1

My localhost folder fills up and overload my C drive space. how do i keep this form happening and what is it used for?

2

you probably have thumbnails for seeking enabled, that’s where they are stored

https://support.plex.tv/articles/202197528-video-preview-thumbnails/

3

See https://support.plex.tv/articles/202529153-why-is-my-plex-media-server-directory-so-large/

and [HowTo] An extended guide on how to move the Plex data folder on Windows