Sometimes you'll see a house that doesn't really work for you -- BUT -- it COULD -- with some major renovations. Maybe that's building an addition, adding a garage, tearing out some interior walls to make larger rooms, etc.
Often, you'll determine that these renovations are possible -- but it is my opinion that they are not always advisable.
A HOUSE JUST FOR YOU -- You should enjoy the home you live in, and make it your own, however a buyer can go overboard here. If you make major renovations to a home that makes it work ONLY for you -- then later when you try to sell, you may find it to be a challenge if your renovations made it work ideally for you -- and extraordinarily less than ideally for every other possible future owner of the home.
OVER-BUILDING FOR THE NEIGHBORHOOD -- If you're buying a home in a neighborhood where homes usually sell for $250K, and you are likely to spend $230K because the house you are purchasing needs work, and then you spend $130K on fixing it up and making it work well for you -- all of a sudden you have a $360K home to try to sell in the future, surrounded by $250K homes.
So -- by all means, consider making changes or improvements to the house that you purchase -- but keep in mind the big picture related to eventually selling the house as well.