When you live alone (without parents to organize the details of existence) you notice things. For me, one of them is about "cleaning up". The optimal state of your environment is "cleaned up", but when you use an object you don't want to put it away Right Now, because it interrupts whatever it is that you're going. You can defer the "put away" action for Later. Later is the time when you "clean up", all at once, thus optimizing the effort, because you have to do less context switching¹. So you have a choice: put it away properly Right Now, or leave it in a messy state for cleanup Later.

Now, this all sounds good, except you have a problem to manage: your Mess. If it gets too big, you can't find things, you don't have room to move around, you find various living creatures sharing your space, etc. So an important skill is Mess Management. One learns it over time; some people are naturally good at it, others are hopeless. I like to think that you trade Mess Credits for time/energy/attention: you defer proper cleanup of an item (taking out Mess Credits) and you have more time/energy/attention Right Now, because you don't have to clean up Right Now. You also avoid a couple of context switches (away from the current activity to put away the item, and back to the activity). Take out too much credit and it's bad. The credit has interest - items left out will gather dust (and maybe living things) and will hamper your activities to some degree.

Now, to the point I wanted to make when I started writing this: an important technique in Mess Management is making the proper mess. It helps both with finding things quickly in the mess, and with cleaning up later on. All you have to do is to organize the mess a bit. When you decide to leave an item in a messy state, you should make a small effort, don't just throw it away. For example, have a single place on your desk where you leave stuff for Later processing (bills, receipts, notes, etc). Or when you bring your groceries home, and are too lazy to distribute them throughout your kitchen, at least make a quick effort to put inside the fridge everything that needs to be there - that way you'll be able to defer the "groceries cleanup" task for longer without major problems. If you're a to-do-list-person it might help to make a quick note in the to-do-list about important deferred cleanup jobs ("throw away empty pizza box from under bed"). And my favourite trick: I set up a keyboard shortcut (using Quicksilver) so that I can quickly write a note and it gets stored in a text file; later I check the file and handle all notes at once. This way I don't really interrupting what I am doing.

Disclaimer: I'm kind of obsessive about being reasonably organized in a lazy way, thus the ideas expressed above. :)