Nothing. fileee is basically free of charge and should always remain free of charge for the normal consumer.
Whoever creates a free fileee account will receive 1000 free start documents for the first three months. After those three months there is a monthly upload limit of 15 documents.
If that is not enough for you, you can upgrade to fileee Premium or Professional. A overview of the services can be found here: https://www.fileee.com/premium/.
The use of the fileeeBox is optional. It is intended for those who do not want or can not discard documents after the digitization. With using a fileeBox you can easily store documents and find them in seconds if needed. Uploads with the fileeeBox are not affected by the upload limit. More about fileeeBox: https://box.fileee.com/.