encrypting live data in SQL Azure
TDE, or &quot;transparent database encryption&quot; encrypts all data contained in the encrypted database.  That is, both existing and newly inserted or updated data is encrypted.
There is no requirement to re-encrypt the database once TDE is enabled, assuming the new data is imported into the same TDE encrypted database.
Along with the document you linked to, this document on transparent database encryption contains a wealth of important information about TDE.
TDE, as suggested in its name, is transparent.  That is, running a select statement against data contained in a TDE-encrypted database will not display encrypted data - it will display the unencrypted version of the data.  The encryption protection is for data-at-rest - i.e. If someone steals a copy of the database, they won't be able see any data contained in that database without the certificate used to encrypt the database.  If you need to prevent data being visible in certain columns such as a credit card number, you should look at column encryption.