I meant, keeping the windows open are bad while running the dehumidifier/filtering.. as it will constantly battle to keep the "fresh" incoming air clean/dry, you might as well switch it off then. Most houses are very "leaky" anyway around windows, doors and so on, so for some rooms it is kinda pointless to use in. So for bedrooms, bathrooms and other smaller areas where you can shut the doors and windows and let it do it's work, it works very well! But a bigger area like an open plan kitchen and lounge, rather just crack a window or buy a larger dehumidifier/filter but then you have to battle noise and electricity usage. If you have pets that sheds a lot of skin/hair, the filter will also clog up faster but you will have less of that animal smell in your place. If you have pets that pee/poo in your house, no amount of filtering going to help you with that.

Overall, I do recommend people still buy one, they are helpful for all sorts of things.