For the life of me I cannot figure out why people insist on putting plastic liners in their cats litter box. It makes absolutely no sense whatsoever for several reasons:
1) Plastic is an unnatural substance for cats to eliminate on.
2) Cats have claws and like to cover up their waste. When they do so, they inevitably rip the plastic liner.
3) When the liner gets ripped, it makes a terrible mess to have to change it.
4) Since the liner does get ripped, the actual bottom of the litter box gets waste and litter on it and has to be cleaned anyway.
5) Cats do not like the feeling of the plastic and often rip it intentionally.
6) The liners never fit properly and become folded trapping excess urine and feces and making it much harder to clean out on a daily basis.
7) It becomes much more costly than just putting the litter directly in the litter box because once the plastic liner is ripped you can't just lift it out and put it in the trash,. You need to use another plastic bag to transfer the liner into so you don't have litter all over the floor as you take it to the trash.
As a professional pet sitter who has cared for hundreds of cats over the years and cleaned hundreds of litter boxes, I can tell you the plastic liners are just a bad idea all the way around.