When a baby is allowed to cry too much and doesn't get any response then the long continued crying that the baby does can cause the babies brain to produce too much cortisol.
When the babies brain produces too much cortisol it can lead to brain damage and possible death.
When your baby is crying you should always go in to see what's wrong with the baby and calm them down or give them what they need or want.
Sometimes your baby just wants to be held and cuddled and feel you close to them and since you're the parent you should cater to the babies needs even if it frustrates you to have to hold the baby when you want to be doing something else.
Babies are a big commitment and if you can't handle the stress of dealing with a baby crying all the time or have the time to properly take care of one them you should not have a baby.
That's just the brutal truth and if a baby is crying never ignore there cries because that's how they communicate with you.