You may object if the request is not likely to get relevant evidence.
The law says that the request must be “reasonably calculated to lead to the discovery of relevant, admissible, evidence.” Something is relevant if it tends to prove or disprove something that one of the sides in the lawsuit needs to prove to win their case.
You may object if the request would result in “unwarranted annoyance, embarrassment."
The key word is “unwarranted.” The judge will weigh the amount of annoyance or embarrassment against the relevance of the evidence, and the need for the evidence in the case.
Undue burden and expense
You may object if the request would be "unwarranted oppression," also known as an unreasonable burden or expense to comply with.
The judge will weigh the burden and expense against the relevance of the evidence, and the need for the evidence in the case.
Calls for a legal conclusion
Raise this objection if the request requires you to do legal analysis and requests a legal opinion. For example, a Request for Admissions that asks you to admit that your defenses lack merit.
You may object if the request is asking for your analysis, strategy, or thinking about the case.
A discovery request can ask what evidence the person knows, but cannot ask what a person thinks the evidence means. Sometimes called “attorney work product,” and this objection applies equally to self-represented litigants.
Uncertain, ambiguous, or confusing
You may object if a request does not make sense, is too vague to understand, or so confusing that it cannot be understood.