In the US (and probably most places) a house is the most expensive asset that a person will own throughout their life.

It is reasonable to ask if a person's life would be better if they were able to extract some of the value from the house in exchange for other things. For example, I can borrow against the value of my home and afford to go on more vacations, or a nicer car. It could fund my retirement, even.

Another way of looking at it is as a component of an overall portfolio. Does it make sense for me to have 80% of my net worth in real estate when I can get a 30 year loan at 2% or 3% and diversify? HELOCs are another commonly used instrument.

I suppose some may argue that a few of the things I've mentioned are "irresponsible", but the truth is that it varies from person to person. When used intelligently, debt like this can be a win for both parties.