What is hoarding? It is not just collecting. For example, those who save stamps are not hoarding. Hoarding is acquiring and keeping things that are useless or relatively useless. There is usually a lot of anxiety in letting go of these useless things. Hoarders generally have problems making decisions about what to keep, how to sort, etc. They seem to process information differently and in a more complex way about filing and sorting. They may or may not have Obsessive Compulsive Disorder (OCD).
Hoarding can lead to social isolation. It also fosters marital discord. When the person is also a compulsive shopper, it can mean financial difficulties. When the person has so much "stuff," cleaning can become more difficult and there can be consequent health hazards.
One of the national experts on hoarding is Randy Frost. Here is his summary on some of the underlying issues which lead to hoarding: