Does a laser toner cartridge have to be empty before refilling?

I would like to know if a laser toner cartridge have to be empty before I refill it. Since I ordered a toner bottle online and the description said it had to be empty.

I emptied the toner and then realised that there was huge amount of powder which came out.

I was thinking there was lot left and so why did I have to empty it?

I want to know that if laser toner cartridge is "empty" then if the then powder inside disappears while printing or if it's just a residue.

If you are refilling with cheap toner into a genuine one, you are probably best off emptying as it will be different and you may have a lot of imperfections when they mix.

If you are topping up one that has already been refilled, I would say the answer is no because it is the same stuff.

Just be careful if you do this to much as they may change the consistency or formulae between batches/bottles.

Lastly, make sure it really is the toner you are emptying and not the waste toner or similar as this would have to be emptied each time.

(Out of curiosity, what printer/cartridge is this?)