Yes. It is to clean out the gunk.
And it really depends on the style of filter. Things like aquaclear pads should not be replaced, IMO. But things where there is a filter pad with carbon in it, as in the case of Whispers or Penguins which have some sort of other biological filter (the biowheels, the sponge biofilter in newer model whispers and tetratecs) are different, IMO. At least in whispers, you can replace the carbon and really clean out the filter sleeve (in old tank water). But penguin filter cartridges are really not meant to stay in the filter indefinitely, unlike aquaclears, and I have rinsed them and then cut them open, and my, there is a lot of gunk in there that remains. The biowheels are the primary biological filter on those.
Realistically, however, in most tanks of this size that are not overstocked, the LR can handle a good deal of the ammonia production, and simply changing a filter pad should not result in a measurable ammonia spike, IMO. I believe the filtration on this tank- the penguin + LR- was marginal for the stocking/feeding going on, and so the loss of even a little bit of bacteria (on the filter pads) resulted in an ammonia spike.
When you consider all of the surfaces in a tank that grow bacteria, and they all will, you can see where replacing two filter pads (which are designed to be replaced), causing an ammonia spike is not typical.
There are people with 55g tanks with 50 lbs of LR who don't run a filter like this at all without problems. And thankfully some of the bioload of this tank is also reduced.