In any mystery, it is important to get to know the suspects.  In this case, the neighbors!

The moor is very sparsely inhabited, and those who live near each other are thrown very much together. For this reason I saw a good deal of Sir Charles Baskerville. With the exception of Mr. Frankland, of Lafter Hall, and Mr. Stapleton, the naturalist, there are no other men of education within many miles. (enotes etext pdf p. 13)

Mr. Frankland lives in Lafter hall (notice the pun on "laughter").  He is basically a muder suspect, though he is described as “an unknown factor” in chapter 6.  Mr. Frankland is a neighbor.  It is noted that there are not many educated men around.  He is ”an elderly man, red faced, white haired, and choleric” (p. 55).  He loves the law, and enjoys wasting his money on lawsuits.

He fights for the mere pleasure of fighting and is equally ready to take up either side of a question, so that it is no wonder that he has found it a costly amusement. (p. 55-56)

Thus Mr. Frankland is described as the comic relief.  He keeps things interesting!  It is also noted that he has a telescope, and a daughter who wrote to Sir Charles but never got his interest.  You could consider Mr. Frankland the comic relief, or a red herring (a clue put in to confuse the reader).

Where does Mr. Frankland live in The Hound of the Baskervilles?

Mr. Frankland is one of the more prominent neighbors of Baskerville Hall. He resides at Lafter Hall, where he is known to survey the surrounding landscape with his telescope. His primary hobby is bringing lawsuits against anyone who has, in his opinion, wronged him.

His lone direct contribution to the story is that he discovers, through his telescope, that a man is hiding in the ancient ruins on the moor and that a boy takes supplies to that man regularly. He believes that this person must be Selden, the escaped convict, but he tells no one about this except Dr. Watson. As it turns out, the man hiding in the ancient ruins is Sherlock Holmes, so it is quite convenient to the plot that Frankland has a  feud with local law enforcement sufficient to ensure that he does not report what he thinks to be an escaped convict living on the moor, but is willing to give Dr. Watson enough information that Watson can find Holmes.

Mr. Frankland’s other important connection to the story is indirect. His estranged daughter, Laura Lyons, is responsible for luring Sir Charles Baskerville to the place where he encounters Stapleton’s hound and subsequently dies of a heart attack.