In the Common Options section you can restrict the scope of the maintenance process(es) to certain albums or tags. You got to un-check Whole albums collection or Whole tags collection to get access to the drop down fields where you can select albums or tags. Note that in this drop down field you have a context menu to select or deselect children and/or parents and also to invert the selection. If you switch from Albums to Tags or vice versa your selection in the now grayed out item will remain untouched which might be useful if you need a certain selection more often.
Since many of the processes the maintenance tool can perform are time consuming (depending also on the scope, of course) you have the choice to check Work on all processor cores if your machine has more than one and they are not occupied otherwise.
This process will scan the collections you defined in → → for new items, i.e. image files you added to your collections while digiKam was not running. You can run this process also automatically on digiKam startup by checking Scan for new items at startup in → → .
Rebuilding the thumbnails might be necessary if you worked on your images with other applications or if you changed the thumbnail size in → → → . The “ Scan for changed or non-cataloged items” option can speed up the process in the first case or if you just added pictures to your collection.
Fingerprints are necessary for finding duplicates and similar items and for finding images by sketches. For detailed description see Fuzzy View.
The Find Duplicates Tool is doing the same as the Find duplicates button in the Fuzzy View, but here you can combine it with other maintenance operations and you have the chance to check “Work on all processor cores” under Common Options (see above) to speed up the process.
This is the same process you can access in the People View with the Scan collection for faces button. Here you just cannot set the Fast - Accurate parameter and the option “Clear and rebuild all training data”. For more information about the Faces Data Management options see People View.
The Image Quality Sorter assigns quality labels to images according to the settings in → → . There you also have to enable this tool if you want to use it. Since it is a time consuming process it's a good idea to check Work on all processor cores and restrict the job to certain albums or tags. The tool will set the red flag for “rejected”, the yellow one for “pending” and the green one for “accepted”.