GnuCash gives warnings when certain operations are attempted, such as removing a transaction or removing the splits of a transaction.
The warning message gives you the option to not give you these warnings when attempting the operation.
Check-boxes labeled Remember and don’t ask me again and Remember and don’t ask me again this session allow disabling the warnings.
This option permits reseting the warnings to the default, IE make the warning happen.
Warnings may be selectivly enabled.