The debt effect of TurnOver stems from when people with inherent knowledge of a system leave a project/company/life -- taking their knowledge with them, and/or their work/knowledge areas are not documented, or not adequately documented for someone else to take over and move into the vacated position.  The amount and quality of productive activity or the replacement will be reduced as they try to learn enough to pick up from where the developer left off.  In theory, this will be smaller debt for more experienced developers, or if the project/code/technique/whatever is well-documented including commented code, notes, design papers, files, paper documents, ...  

If all you have are green new-hires, and a major person leaves, TurnOver debt can be enormous.  Without anyone to provide guidance, insight, or at least encouragement, the learning curve can be quite steep.  Moreover, TurnOver debt can have a higher compound interest rate if the project is not managed well.  If a key person leaves, and too junior a person is put on that project, there is additional pressure on the replacement.  If resources are strained already, stretching them further can leave to drastic problems (hemorrhaging) if the new developers decide that "it's just too much", management isn't engaged (positively), they still have their original work areas to support, etc.  There may be a series of job descriptions leaving a project in a short period of time -- kind of a late payment penalty.

TurnOver can be related to SpinUp (an example of SpinUp debt is when a developer(etc) moves into a new area either outside of their expertise or into new techniques outside of their expertise.  The a portion of the resource's time is spend just trying to come up to speed on a project -- to get to the point where they know enough to actually contribute enough to offset their sponge cycle).

Our examples of both SpinUp debt and TurnOver debt:

SpinUp:
We had some very sharp new graduates hired for an on-going project and essentially thrown into the abyss.  They had brains and some techniques from college, and were put on a project with no background, no documentation, no support, no senior developers for guidance, no customers to talk to, and left to learn for themselves.  It took them almost a year to learn the background information of a communications system they were writing code for.  They knew coding and where given data with no clue as to data or relationships, no data dictionary, no training on the data, the application, or the system that they were coding for, no users who could explain, review, or validate their results.  For the most part, they had no requirements other than "we'll know it when we see it".  They would try to analyze data that they had no idea about, and then code packages for ETL.  Their customers expected to get a finished product.  The developers would schedule an electronic delivery of processed data, and would receive not much more than "it doesn't look like it should".  

TurnOver:
As the contract took on more tasks, as the same developers were trying to come up to speed on their areas, they were expected to be productive and also take on new totally new tasks outside of their expertise.  There were no more hours assigned and not much feedback from management other than "Is this done yet?  Why not?"  After several cycles, one of the sharp -- not necessarily highly experienced -- juniors left.  He left no documentation behind, partly because he was given no time, and there were no requirements to do it.  And his duties were re-assigned to another developer -- who now had to re-learn what the other guy had done (what as well as why).  And then that developer got fed up and left, with no additional documentation.  And with HIS duties (original and inherited) being passed on.  And THAT co-worker left.  This is hemorrhaging.



There will ALWAYS be some effect from TurnOver, even if it's that someone new has to learn which coffee blend the office prefers, who has it, who roasts it, what grind, etc.  Don't under estimate Coffee Quality (Pizza Quality, etc.) as a production factor.  Lack of guidance, lack of input, lack of LOGICAL requirements, and the time to do them in all are factors in both TurnOver and SpinUp debt.  And companies keep accruing it.