We have 231 services and 10 hosts with disabled notification on Icinga as of now.
I'm also adding DBA because quite a few of them are DB-related, but not only.
In most cases the the host itself and other checks have notifications enabled, just few checks have them disabled, without any related message that explains why.
Please review the list of them available here and re-enable notifications when possible or add a permanent message that explain why it is disabled, it help when debugging issues/pages.