How can I describe what a Change Order is?  Here goes:

Imagine going into a fine restaurant, ordering the filet at 50 dollars, and then while you were eating, having the waiter come back to your table over and over again explaining that the chef didn't realize that his cost of the filet was higher, that the cost of the gas to run the stove went up while he was cooking it and the busboy asked for a raise right after you ordered - so that 50 dollar filet?  Well they were now charging you 110 dollars.   Sounds ridiculous?  Well, in the traditional model of a renovation, this goes on every day.  

There is nothing that strikes fear in the hearts of people about to renovate than the horror stories of how change orders can derail budgets and absolutely crush schedules.  

Change orders kill projects.  Period.

They are very unwelcome surprises and the easiest way to avoid them is to be sure to work with a Design / Build firm that prohibits them - unless you and only you change your mind on a specification or scope of the project.  There is no place for a change order in a well-orchestrated, well-designed and well managed project.  I cannot imagine how any buyer of a property can possibly establish their own budgetary priorities, not knowing how much their project will escalate as it goes on.  And lastly, and possibly most importantly - architecture and design firms that do not prohibit change orders are using them as a primary source of revenue – rather than properly budgeting and bidding the project from the outset.  We call that “the seduction” – which never, ever is satisfying.

Short of that, I believe it's the absolute worst part of any renovation and one should avoid them at all costs.