If you look at the pec muscles the origins and insertions there is a strong argument for declines. I wouldn't do declines without a spotter. I use dumbbells so I can dump them. As a bonus guys with bad shoulders often find they cause zero pain. I know that's the case for me.
The barbell bench is an over used exercise. It has caused so much damage to trainers. Can't count the number of big time bench press guys whose shoulders and pec tie ins were ruined. It leads to a loss of flexibility in the joint then tears can happen. Sometimes even the elbows go on guys. It is the most popular lift. When guys ask how much can you lift it's always referring to the bench press. Damn there are 200 other ways to lift. I think it's popular because what other exercise can you do lying on a bed? I'm way more impressed to hear what a guy's power clean is over a bench. At least I know the guy is explosive, has a good vertical leap and can sprint. A big bench shows nothing of athletic potential. It's popular in the NFL combine because of the clueless that wanted to see it the most popular lift.
Having said this there is nothing wrong with including it in your routine. The problem is when you build your routine around the bench press.
If you want to train your pecs hard but not stress your rotator cuffs then try the decline press. Your screaming shoulders will thank me.