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This is highly dependent on your location.

From what I've been told, in the UK, shelters won't let you adopt a cat unless you agree that it will be allowed outside.

In the US, many/most shelters won't let you adopt a cat unless you agree that it will NOT be allowed outside.

Part of this is likely due to more cars being driven at higher speeds by inattentive people in the States (that's the main reason I don't let my cats out, I have seen way too much roadkill in my life and it sucks every time, those deaths are not always quick). Some other reasons not to let them out would be increased chance of disease, unwanted interactions with neighbors and the needless decimation of local wildlife.