Functional training isn't solely for athletes, don't let the heading fool you. In simplest terms it is a form of training utilising multiple joints across various planes of movement. As such it assists with strength and endurance for everyday activities.
From upright rows to lifting the contents of grocery shopping onto a kitchen counter. This is fundamentally what functional training is.
Thinking about it logically your performance is based on your capability to complete the task undertaken. Tasks occur in every facet of our lives whether it is grocery shopping, work or sport. If the objective you set out to complete is within your level of ability it can be achieved, this is made easier the better you are at the given task.
To expand upon this if you were able to complete a 1 RM(Rep Max) bicep curl of 65kg and your daily chores meant you needed to complete a number of 65kg lifts you might be able to do it, however, the hazard of you failing increases as does the risk of injury since every lift brings you closer to the edge of your limitations.