As OpenERP / Odoo is free, you have no limitation to use it.

Its License with AGPL V3, with Exceptions. It mean you can't change their branding and their titles in your server.

Also as you use some private module or purchased code or person developed code must needed to share to public figure as free.

Its too good to use private OpenERP Cloud so your customer data not utilize by any other one, where On odoo's cloud, their is no gaurantee.

Odoo is 100% open source and therefore can be used without limits on users.

What is available is a series of services: one click installation of modules (apps, via the Apps menu), unlimited helpdesk (functional support), unlimited bug fixing, upgrading your database between major versions (so you can take advantage of the software upgrades), security alerts, as well as the right to develop and not distribute 'private use' modules if you choose to do so and agree to keep them undistributed.

Without a paid subscription to these services, you will need to manually install apps/modules if you have more than two users in the system.

This question has been discussed MANY times on this forum, I suggest you review the existing answers for more information.