What is load last sets?

You can use the load last sets to override sets defined in your workout routine. If you enable this (under settings > workout settings) Fitlist will load the last logged weights instead of what was originally specified in your workout.  

This can also be done on a per exercise basis by tapping the '...' icon on the logging page exercise by exercise in your workout. This will override just the sets for that exercise with the last logged values.