eCognition can slow down when you are having numerous features displayed in the "Image Object Information" window. When clicking on an object, it will calculate all features that you have chosen to display in this window for the selected object. At some point this can take a bit of time. I like to "swipe" all features that are displayed in the "Image Object Information" window from time to time (as they pile up when I develop a rule set).

How to do it?

1. Right-click into the "Image Object Information Window"
2. Choose "Select features to display..."
3. Remove all features from the selected right side of the "Select displayed features" window via double-click and click "OK"

This helps me to keep a better overview and it also improves the performance while developing. Enjoy!