There is always the issue of having to be very careful when training new users on your salesforce.com system.
It will usually require you to sit beside them and watch them like a hawk in case they enter something incorrectly when ideally you would like them to become comfortable with the CRM by playing with it themselves to become familiar.
Why not let them go crazy on a sandbox.
Almost every license type on salesforce.com will provide you with either a partial copy of your data and CRM configuration or a full copy.
This link explains what you will have allocated to you in the way of sandboxes with your own license types.
Salesforce admins have access the four types of Sandboxes, these are:
1 . Developer Sandbox — This type of Sandbox is used for developing and testing in a hidden environment. It keeps the copy of your production organization’s metadata.
2 . Developer Pro — It has larger storage limits rest is almost similar to the developer sandbox. Developer Pro is best for more robust testing.
3 . Partial Copy Sandbox — This Sandbox is designed for testing purposes, it includes configuration data and a subset of production data which defined by you.
4 . Full copy Sandbox- This type of Sandbox is a live copy of your Salesforce account. Full copy Sandbox is provided in Enterprise version of Salesforce and is perfect for load testing, production testing and production deployment staging.
Type 3 and 4 are perfect to use as training environments.
Once it is created, add your new users to the sandbox and let them happily use the system knowing with the click of a button when they are done it can all be refreshed back to a clean copy again afterwards.