I don't know about the mode so I am not sure what the default mode is. All I know is that when you start messing with Mechanism, you get failures all the time due to the state the assembly is in when you run the Analysis. It took longer to figure out how to minimize these problems than anything I've had to clean up from this.
But all too often, Creo decides at a later stage that it has problems. Just ran into one where the exploded view made the assembly constraints fail (huh?)... I was certainly not at a stage where I could go address it right there and then, but the persistent error on the message line made me go back and fix it.
What's worse is the multitude failures when you work with advanced assembly states in drawings. Regen errors abound when you have many models in the drawing in many stated of explode, flexible models, and sections. If these errors stops me at every turn, I'd be buying new laptops on a weekly basis.
So yes, I believe a model should be "verified" by whom-ever is expected to sustain it and if someone checks in a file that is full of errors and holes, they would either get a very stern talking too or find themselves looking for new employment... in the case of contractors.