Larger than average gardens, existing outbuildings and land can be very attractive features of many rural properties for sale. If you are looking for residential/commercial development or conversion potential though, have an early discussion with the relevant local planning department first as you should never assume permission will be granted or straightforward.
Similarly, find out whether the property forms (or previously formed) part of an estate, as restrictive covenants may require past or future property owners to obtain the estate owner's consent to any alternations or improvements. You should also check for any unusual access rights. For instance, if you need to pass over green verges, a village green or common land to get to the property, you should clarify whether you have legal access to do so (on foot and in vehicles). It's also important to find out if there are any public rights of way over any of the land that forms part of the property you're thinking of buying.
These are just some of the many issues to consider, but a good solicitor who is familiar with the potential legal complexities of rural properties and has a good knowledge of the local area, will be invaluable in helping you avoid the pitfalls.