I currently have an email address, firstname.lastname@example.org, that I currently use to forward to a gmail account that I've used for years. I currently have it set, so I can send email from my email@example.com instead of firstname.lastname@example.org.
This is done through the web ui on my current domain name, provider, gandi.net.
What are the main differences between this arrangement, and setting up a
Google Apps for your domain setup, where I'm explicitly listing in the dns records to point records to point to Google's app mail server?