The benefit is a much more prepared offensive for the TH9 world ahead of you. You will have a better chance of finishing your heroes earlier by the time your base is maxed.
Yes, you kind of are a sitting duck to TH9 attacks in terms of farming. But this strategy isn't meant for the people who attack only once and get off immediately.
In war, if you get 3-starred, that shouldn't really matter at most. Most TH8s are 3-starred during wars, why does it matter if you're 3-starred and still have the weight of a TH8? Besides, trading in on being 3-starred for 6-stars earned from attacking in war is much better then being 2 starred as a new TH9 with xbows but getting only 0-1 stars from attacking.





