How does Holmes's suggestion to bring a revolver affect the mood of "The Adventure of the Speckled Band?"

Many of titles of the Sherlock Holmes stories contain the word "Adventure." Sir Arthur Conan Doyle, following the example set by Edgar Allan Poe in his stories involving C. Auguste Dupin, especially "The Murders in the Rue Morgue," wanted his detective tales to contain investigation, deduction, unusual characters, and action with some danger. It can be noted that although Sherlock Holmes is often portrayed as a rather languid armchair detective, he shows himself capable of vigorous action in most of his stories. For example, he is the one who disarms and captures the vicious John Clay in "The Red-Headed League."

In "The Murders in the Rue Morgue," when the sailor offers Dupin a reward for the recovery of his Ourang-Outang:

“Well,” replied my friend, “that is all very fair, to be sure. Let me think!—what should I have? Oh! I will tell you. My reward shall be this. You shall give me all the information in your power about these murders in the Rue Morgue.”

Dupin said the last words in a very low tone, and very quietly. Just as quietly, too, he walked toward the door, locked it, and put the key in his pocket. He then drew a pistol from his bosom and placed it, without the least flurry, upon the table.

This is a prelude to a long story about how the the Ourang-Outang killed the two women in the supposedly locked room. Dupin had previously given his friend two more pistols which his friend was keeping ready but out of sight. The pistols are never needed, but they add an element of dramatic suspense and danger to the sailor's story. Poe established a convention which has been followed in countless mystery stories and mystery movies ever since. The main purpose is to keep the story dramatic. Drama is always based on conflict. Pistols symbolize potential conflict. Poe understood this. Doyle learned it from Poe.

In "The Adventure of the Speckled Band," Dr. Grimesby Roylott is only seen once alive, but his menace haunts the entire story and keeps the reader wondering whether he might show up unexpectedly, as he did at Baker Street, and catch Holmes and Watson snooping around right inside his own house. A man like Roylott would be sure to have a number of guns on the premises, both for hunting and protection. If he caught Holmes and Watson inside Stoke Moran, he might try to kill them on the principle that "A man's home is his castle." Such a confrontation never comes off, but it adds drama and "adventure" to the detailed inspection of the exterior and interior of the premises.  That is why Holmes tells Watson:

I should be very much obliged if you would slip your revolver into your pocket. An Eley's No. 2 is an excellent argument with gentlemen who can twist steel pokers into knots.