I have built wheels for about 10 years now, at some point I was building many of them, now only build for myself and a few friends and colleagues.
IME you want a pair of handbuilt wheels if you don't fit the stereotype of skinny rider who wants to bag KOM on Strava... so if you are heavy, if you want to ride long distance, if you want to do cycle touring... for all these reasons, the reliability of hand built wheels trumps and factory wheel out there.
There is also a market for reasonably priced carbon wheels, which is not catered for by Mavic, Fulcrum and Co. and it is catered for by some builders, like Malcolm above, as well as Wheelsmith in Scotland, JRA in Sheffield and a number of others.
BUT, if you are 65 kg and only ride 2,000 miles per year chasing KOM, then you are better off getting a pair of Fulcrum or Mavic or whatever is on offer at the time