Modifying a workitem with IOperationAdvisor or IOperationParticipant ?

Thanks so much for your prompt response Ralph... 

Hi John,

Update

You should use a Participant/followup action to modify a work item, not do it in a precondition.

Update

Old Answer
I am aware of the difference and have thought about its implications. I would assume that it is save to modify and save the work item itself in the precondition. What will happen is that the save triggers the preconditions again. So you might want to pass a cue that the precondition is triggered by a prior precondition save (as described in the example).

Other than that, I would be more concerned about what the user sees in the UI. Does it refresh the change? I have not done this myself, but I would definitely try it out - on a test system as described in the Extension workshop. 

Old Answer

Please, can you share your experience here?

+1. Preconditions shouldn't make modifications to the data.

Sam, Jared thanks for the hints. I updated the answer with your input.

Are there any underlying reasons/implications why? The reason why I am asking is that there are other activities going on before the save. For example value providers.

I am aware that precondition really says condition - which is a test and not a manipulation. However, I can see reasons why someone would want to modify items before they are saved. For example to set dependent values. I am also aware that there are value providers available and you can create such extensions. They only appear to be much more complex than Advisors.