Don't confuse mandatory, with the examiner looking for evidence that you are reasonably diligent and well across your preflight planning to a safe standard.
Exactly this.
When I examine for a revalidation prof check, I would expect mass & balance, performance, and fuel plans to be completed. If they are not, you can bet I'll be asking some indepth questions to assess whether it is due to complacency or lack of knowledge these items were not completed.
If you come out with 30 l/hr fuel burn, the first question will be where you got that figure from. If you say "my instructor told me 32 so I just rounded it down" you can bet I'll be saying lets take a look at what the POH says, and get you using the graphs to calculate actual fuel required.
If however the answer is I have looked at the climb graphs, and taken a planned 75% power at 2000', and rounding this up gives a conservative fuel burn of 30 l/r, then I probably wouldn't go to the effort of getting the POH out and trawling through it, as I would know the expected fuel burn myself, and you have demonstrated knowledge and appreciation of the aircraft performance.