Depends on your skills.
Quite often it is down to how you will repair
If as above a deraillerur broke, I would remove the chain, remove or cable tie the dérailleur t a safe secure position, shorten the chain to a mid level gear and ride home in that gear
So for this case a chain splitter would be appropriate. However if you are not comfortable splitting and reconnecting a chain, then there is no point in carrying it
Quite often it is down to how you will repair
If as above a deraillerur broke, I would remove the chain, remove or cable tie the dérailleur t a safe secure position, shorten the chain to a mid level gear and ride home in that gear
So for this case a chain splitter would be appropriate. However if you are not comfortable splitting and reconnecting a chain, then there is no point in carrying it