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Which is just another way of "mixing" your bitcoins and hiding their source, and which results in fees for both you and your landlord as you convert bitcoins to local currency and your landlord converts the local currency back into bitcoins. Furthermore, it may be difficult to send the cash to your landlord if he lives far away or isn't around much, while bitcoins are quite easy to send.
You don't "need to". It's up to each individual to decide how important their privacy is to them, and how much responsibility they want to take for controling their own wealth.