Out of all the maths that people did at school,
why do they so often say that the times tables are the most useful?
I agree they can be useful.
If you know how to use them.
If you don't know how to use them
they're not useful.
I also find really useful:
addition, subtraction, angles, simple graphs, if a plus b = c and a plus b = d then c = d, and symmetry...
I've always liked symmetry.