Loss carryforward means you don't pay a performance fee on profits that only recover earlier losses.
CNKTID tracks it separately for each strategy you copy. Example at a 10% fee: you lose $100 in one month, then make $150 the next. Only the $50 above the earlier loss counts, so the fee is $5, not $15.
Losses in one strategy don't reduce fees in another, because each trader is paid only on what their own strategy earned for you.