Why it's on the list: For the majority of lifters, the machine chest fly (aka, pec-deck) is a more effective, harder-to-screw-up alternative to dumbbell flyes. If your gym has one, it's a great move to get a great pump without having to balance any weights or put your shoulders at risk.
But does it work? EMG data shows that activation of the pectoralis major is statistically similar between the machine fly and bench press, which means that even though you'll likely be working in different rep ranges for each exercise, both are worthy components to chest day. The big difference? For the machine, you don't need a spotter and can more safely push the intensity and reach true muscle failure.
In your workout: As a pre-exhaust, hit a few sets of 10-15 before your presses.As a burnout, hit the machine fly last in your routine for sets of around 10-12. Experiment with dropsets, partial reps, and other intensity boosters. Don't be afraid to take this movement to failure, and know that you've earned your post-workout protein shake.