Disadvantage is you may be targeting yourself for the government. Another disadvantage - it may make things more difficult/complicated for the recipient.
Depending on the contents of a particular email, it might either be a good idea, or a waste of energy.
If security is only needed occasionally, you might encrypt a document and then send it as an attachment to an unencrypted email. If you regularly need to send ss numbers, bank account information, or other info best kept confidential, using an encrypted program might make sense.