Step 1: Concept
Sentences can be categorized by their communicative function (e.g., asking, ordering, advising).
Step 2: Meaning
The speaker is offering guidance on what is "better" for the listener to do, supported by a reason ("waste of time").
Step 3: Analysis
Providing a helpful direction about future behavior for the listener's benefit is the definition of "advising."
Step 4: Conclusion
The primary function of the sentence is to offer advice.
Final Answer: (A)