There aren't really any cons. The main thing to watch out for is what happens with your DNS hosting. Most domain registrars provide free DNS hosting when you register a domain, but if you transfer the domain out, they will likely cancel the DNS hosting, and you will no longer be able to receive emails. Or, a less likely but possible problem is the new registrar will change the DNS servers to their own when they receive the domain but don't set the MX records up for your email.
So if you are using your current registrar's DNS servers, you need to make sure your new registrar has DNS servers correctly configured ready for you to use.
The only other thing to worry about is the expiry date of the domain. .com transfers can easily take a few weeks to go through, so if your domain expires soon, you need to get on with it. Most registrars will renew your domain for one year when you transfer to them as a means of charging you something for the transfer.