What is the relevance of including various episodes in Tom Jones?
In the most general sense, the relevance of these episodes is structural and thematic. That is to say, the novel blends structures from epic poetry and from the picaresque novel (such as Don Quixote). The first leads readers to expect adventures; the second leads readers to expect rambling and almost disconnected episodes. Therefore, regardless of the content, the episodes fit the form, like cliffhangers or dramatic announcements in soap operas.
As far as specifics, the reasons vary. For example, in Chapter 3, the scene with Mrs. Partridge is humorous, and intended to parody various period concerns (education, fidelity) and conventions (the confrontation scene).