They should be part and parcel of your toolbox.
Even if you do not know the full information inside out, what you should know in the least is where to access the information from within them in very little time.
We can't possibly memorise every last detail from these books, but them more we read them and apply the rules from them, the more our brains will store that information, and over time, it gets set in stone in our brain.
But if you've not recently picked one up, or in the least read through one to know where to access the information, how will this look to a pupil when you are fumbling your way through one to give them an answer?
These books pretty much cover every subject you will need for the average learner driver, and the core skills to become a driving instructor. There are other that you can use if you get into advanced driving tuition, but without a doubt these are your bread and butter.
Have them to hand for every single lesson.