* Forward as New lets you re-send a message to different recipients. It opens a new draft using the current message's subject and body, but leaving To, Cc, and Bcc blank.
* Compose to Same lets you compose a new message to an existing group of recipients. It opens a draft with blank subject and body, filling in To, Cc, and Bcc from the current message.
* Send Similar lets you update a recurring message to a group of recipients. It opens a new draft using the current message's To, Cc, Bcc, subject, and body.

Gmail is great, but some common things take a lot of steps. For example, to resend a message to a different address without the add-on, you would:

1) Click 'Forward'
2) Select the first 9 lines
3) Hit 'Delete'
4) Choose 'Edit Subject' in the dropdown
5) Select 'Fwd: ' in the subject line
6) Hit 'Delete'
7) Get on with life

Not the end of the world, but after the 50th time you want something quicker. With the add-on, it's one click!