While we don't always use ultrasonic cleaner during the post-cleaning process, there are situations where it can be convenient:
1) Models with lots of deep recess and hollows that are hard to reach
2) Lots of small models that would take too long to do by hand
3) Working with resins that are easy to wash
4) You need to clean at a higher temperature
Ultrasonic cleaner heats up during operation even without a built-in heater, which helps with cleaning but poses a problem when using a flammable solvent like 90% IPA. This is particularly a dilemma in winter where some locations can experience below 10C temperature that will significantly reduce cleaning performance of alcohol but warming up alcohol also poses a fire hazard.
What do we do here?
NASA Scientists proposed using plastic bags
This prevents the flammable vapor from escaping while still getting the benefit of ultrasonic cleaning. In this scenario, you can likely improve cleaning by getting the water temperature up to 30C.