Up:

No Space needs to be taken on your MacBook Hard Drive

Downsides:

Lock outs if you send over 500 emails in a day.

Incorrect sender tag resulting in your mail being flagged as spam or the dreaded “sent on behalf of” message.

8GB Limit for your Mailboxes
Dreamhost is Unlimited

25MB File size limit for sending or receiving
Dreamhost is 40MB