The reason disorganization is a problem is due to waste of time that occurs due to this issue. A disorganized person will always be losing things, won't know where the keys are, he may have to get replacements for important documents etc. This means that when he needs something, he doesn't really know where exactly it would be and hence waste a lot of time looking for it. Hence he becomes less efficient and less effective. This is because there is no system which can be followed.

People need a system in order to be organized. At work, we need to know when to make important calls, which task has higher priority, where must all important documents be stored etc. This is called a system and there must be one in order to live a more...

Disorganized people generally have no such system. They do not have separate storage places for books and tools and hence everything is stashed in one big storage place and it then takes forever to look for a particular item.
Hoarding is another major problem with disorganized people. They have a compulsive hoarding problem and hence they do not throw things away easily. It must however be remembered that the key to organization is to have as little clutter as possible and to minimize clutter, one needs to get rid of things. Disorganized people can also learn a lot by observing organized people and their habits. It's always good to make a serious effort at becoming more organized initially and then it will become a habit.