Assuming the following senarios,

1- The project is already delayed or over buget, and you dont seem to find a way to solve what do you do, do you create a change request to get a new schedule and cost baseline?

2- Some project activities are delayed you know you can make up if you switch resources around, do you create a CR or go to ICC?

3- Assume some employee will be suddenly absent for 2 weeks, his tasks are not on the critical path and if they were delayed for 2 weeks, will not affect the end dates, you want to change the schedule to accomodate for that.. do you need a CR, do you need to go to ICC, do you need to go to the change board?