this is really helpful in making variations - you can loop out a smaller segment & use cmd + j on the resulting extended clip to make a larger loop. change a few things & you've got a more dynamic loop, wham!

another way to do this when you just want your smaller loop extended is with the "dupl. loop" button to the left of your midi. this has less steps than the above method, of course, but presumes you want your full clip looped as a starting point, which isn't always the case. as always, the most appropriate method will vary between situations.