Lets be honest leaving the little filler cap key on a ring with your immobiliser fob is no issue, neither is unlocking / locking it to fill up. It takes literally 5 seconds. If thats too much hassle for you then fine, but its no issue.
Its one of those things that hopefully are never needed but may save a LOAD of hassle and cost one day.
In the end its upto you. Ignore / omit if you wish, but you never know. For the price it seems unwise to take the (admittedly small) risk. I don't want to get stuck somewhere or have the fuel adulterated and damage the engine. Could be costly and you'd never know till the damage was done.
But thats just my opinion.
Atom 4, Clio v6, & some other cars obviously.