Good question.
I happen to like to have things organized.  I like the Motorized Simple machine sets and the old Team Sets for that reason.  I have the Cities and Transportation sets color coded.  Each piece has a dot of fingernail polish.
The Teams sets I have used in camps lately I have kept one on each table. Well, actually with my stuff I never have any pieces "on" the table.  Each piece is to be in a model or in the set - I just call the lid part of the set as it has a nice rim around it to keep pieces from falling on the floor.  For sets of materials that do not have a place for every thing, I have figured out some logical arrangement.  Then I put one of each piece on the copy machine in the spots and Xerox a placemat.  Then I write the number and Xerox copies.

I keep a extras box of needed little pieces and any time any one finds a loose piece they put it in there.

From what I have read on the web such as the FLL forum, most people just dump like pieces in bins and kids pick what they want.
I think it is how the LEGO company is wishing because that would take a whole lot more pieces.
Some parts of real life have a limited amount of resources. ( Such as the amount of money I have.)
So I like to have each group figure out how to make the projects work with materials from one set.
That means they need to keep all the pieces and not loan out or lose any.

Different people have different styles.  Many ways work.