Is TDE needed for index only tablespaces

Hi. We are planning to encrypt all of our databases using TDE and the following syntax. We have some tablespaces that only contain indexes. We want to know if it's necessary to encrypt indexes? We will be encrypting all of the underlying tables, but if there is no actual data in the indexes we will not waste the space/time encrypting them. Thanks.

alter tablespace $1 encryption online using 'aes256' encrypt;