Notes Writer storage space too big and the app is a bit slow?

You can reduce the size of Notes Writer storage data by deleting all the files in the "Trash" location and "Automatic Backups" as well. This could improve the general performance of the app when you have thousands of files on it.

You can also switch off "Automatic Backups" setting of your documents in the "Settings" menu. 

How to check the storage on your iPhone, iPad, and iPod touch?
https://support.apple.com/en-us/HT201656