Why did Mr. Neville St Clair always disguise himself as Hugh Boone? How did it benefit him?'the man with twisted lip" by Conan Doyle The...

The reason that St. Clair always disguised himself was that he could make a lot of money by doing so.

St. Clair was a good actor who found out that he was able to impersonate a disfigured beggar with a twisted face.  By doing so, he was able to make a lot of money.  This allowed him to marry and to buy a very nice home in the country.  He would not have been able to live so well on the salary of a journalist.

So, by disguising himself as a disfigured man, he was able to make much more money than he could any other way.