Maybe something (contrived) like this providing no-op defaults?

  total = calculateOrderTotal(user.order);
  if (user.isPremiumMember) {
    total = total * 0.9;        // 10% discount

versus

  total = calculateOrderTotal(user.order);
  discount = calculateDiscount(user);  // Returns 0.9 or 1.0
  total = total * discount;

Didn't you just shift the branch to the calculateDiscount() function?

No, because the point is that the branch version does not touch "total" when the branch is taken, but the non-branch version will always multiply "total" by something.

Not necessarily.

   return 1 - user.isPremiumMember * 0.1;

would also cut it.

OK, or maybe...

  total = calculateOrderTotal(user.order);
  total = total * user.discount;

Or:

  total = calculateOrderTotal(user.order);
  total *= user.discount;

or:

  return 
         calculateOrderTotal(user.order)
       * user.discount;