Such a complex area, there are so many talking points. I'm far from the best person to comment but I'll throw my thoughts in.
Each individual piece of wood has an optimum pressing point, the perfect amount to get the best performance out of the bat it is made into. 'Ping' is generated from the natural elasticity in the willow fibres, rebounding the ball back from whence it came. Pressing helps to 'toughen up' the wood making it more resilient, whilst maintaining that springy pingy loveliness we all crave. There are some interesting side points here though. A quick example is butterfly stain. A butterfly stain is much harder and less elastic than normal grain structure, and if you have ever used a bat with a butterfly, you"ll know the ball rockets off this harder area.
A harder bat may take a while to get going, but should perform just as well once it's been used for a while. Not a fan Of the term 'opening up' as the true meaning of this is when the grains start to break apart and eventually the face slides off, the sign of a bat at the peak of its powers.
Generally Laver and Wood bats are considered quite hard, mine certainly felt it at first, but the more I use it, the better it gets. Are bats pressed harder for better durability? Who knows.
Asian (especially Pakistani) made bats are drier, definitely. They aren't necessarily softer. The generally perform well instantly but may not last as long due to the dry/brittleness.
Knocking in is important to protect the wood from the damage a new ball can cause when batting. The most vulnerable areas are the edges and toe, but the middle Can be damaged by a prominent seam too. A scuff sheet is handy to help protect the middle of the bat if you don't wish to knock it in. Knocking in also helps to get a harder bat going, see my previous point about the more you use one, the better it gets.
Notice I use words like 'May' a lot, because there are no hard and fast rules here. Willow is a natural product.