Depends on type of dog. I love ours anf would never be without him now but if i could go back in time i wouldnt have gotten one.
Ours is a small lap dog so we dont kennel him which means we are very tied.
People will offer to help out before getting one but change their mind once it becomes a reality.
They develop habits that are very very hard to break. Ours marks his bed daily. He also marks the sofa / carpet if he is left alone downstairs for longer than he would like e.g. if going for a shower or sorting washing. I feel our house constantly smells because when you cant see it you dont always know its happened even with the best will in the world.
They are very expensive. Even more so then i thought for insurance,specialist food, treats, toys, beds, vet checks, jabs, wormers, flea treatment, nails clipped,dog walker, safety equipment. The list goes on.
They also dont always listen. Ours is very stubborn and if he starts barking it can become a bit of a screaming match.
I appreciate some of the above might be able to be ruled out with more intensive training but theres always a chance it might not too.