An old Kentucky 19th century homestead still maintains several of its viable working outbuildings. One of its outbuildings is this small old vertical board shed that's original use is unknown. But today it serves quite nicely as a home gardening shed. It still stands strong upon its original location.
Ideally, one should leave original outbuildings upon their original sites. Old decaying outbuildings could be considered for removal with the owner's permission. Below are a few examples of some that were removed.
I have a friend that has an old outhouse that she bought and had delivered to her backyard garden area. She uses it today as a garden shed.
Another friend loved the old outbuildings that doted the landscapes in Michigan. She asked her husband to find her one and have it delivered to their property for her birthday. On her birthday she got what she wished for. She drys herbs and flowers and wanted the outbuilding for that purpose only -- sorta her studio to be alone with her interests.
I wish that old farms could maintain their outbuildings so they wouldn't fall to decay. However, many times there are either economical or physical reasons why they cannot be kept viable.
I feel the next best thing to decline is finding new homes for them where they can be appreciated and folks driving by can have the opportunity to see a little bit of our farm history.
If you do remove a building from an old farmstead take photos of its surroundings for historical purposes. Your local historical society would be interested in copies of the photos (and perhaps a history) for their archives.