Seedbox is never a requirement, lots of trackers prefer long term seeders over seedboxes. However without a seedbox, you won't be able to take much adventure on seeding back newest torrents for a good ratio, so you will need to use other ways to get a good ratio. There are plenty of ways, like:
- download freeleech torrents
- seed lots of torrents for long time
- upload new torrents
- cross seed torrents
- complete requests
It's only important to build up buffer before you download what you want and not after that