Mandatory “true” has some implications for the config. Must always be there, not upgradeable.
Must expressions can touch the entire config, even config=false data. Evaluating them can be very expensive, care has to be taken when writing them. Dependency expressions are essential. They may easily become a performance hog. Adorn with tailf:dependency expressions. Easy to get a slow system since ConfD cannot know which expressions to evaluate.
Unique needs to be used with care. The code becomes quadratic when large number of instances are added. Use with care.