When many Baloo indexing settings are changed, running worker processes don't respect those changes until they are killed and re-launched. Right now Baloo does not do this, or notify them immediately of changed settings in all cases.
It should, and that would be ideal. Until this happens, let's warn users about this and prompt them to reboot, so they aren't confused by why their changes to indexing settings aren't taking effect.
This message can be removed once https://bugs.kde.org/show_bug.cgi?id=462009 is fully fixed by applying changes live.