That's why it's best to take them out of circuit. But what lighting specialists don't factor into cost is labour.Remember that a ballast within a luminaire uses a significant amount of power.
Replacement of a 250w sodium with a 50w "corn" lamp may not actually reduce consumption by 4/5ths.
A lighting expert would be able to work out the actual savings but it as long as it is cost effective then go for it.
We've fitted some led cobs into some 400w high bays.
Not bright enough for horse arena purposes.
Had some massive 250w compact fluorescent lamps in other fittings, good and bright but very unreliable.
The company sent 6 more FOC after we complained but the replacements were just as troublesome.