Removable liners are ideal for removing at the end of the day to let moisture evaporate or wash and hang dry without having to wash the entire glove which would take a lot longer to dry.I suppose they're removeable so you can swap or replace them? Personally I don't like removeable liners at all, since (for me, and my typically damp hands) they tend to bunch up in the glove, or pull out of the glove, when I don't want them too. And I take my gloves on and off fairly often throughout the day.
Also having a thick removable liner and a thin removable liner means greater flexibility for cold and warm days.
I have also had felt liners pack out and then replaced them with wool liners because the shell was still good to go.