@IOTrav, the work is done by the cc3000 and associations are done in a first-in, first-out way with a max of 7 credentials being stored. The cc3000 will attempt to connect to the stored SSID with the strongest signal level and will stay connected until it loses that connection. So, going from home to work will be straight forward. However, roaming in a place where you have overlapping access points, the cc3000 may not “hop” as expected since it will not re-evaluate its connection until the existing one has dropped.
As for credentials, you can explicitly program them (as in your code example) or by setting them once and allowing the cc3000 to store them in one of its 7 “slots”. 