Final answer:
It's important to question the legality of a decision in cases of potential civil liberties infringement, the need for judicial interpretation, interactions with law enforcement, and when previous court precedents or judicial conduct are involved.
Step-by-step explanation:
One would want to question the legality of a decision before acting upon it in a number of situations. This is crucial when a decision may seem to infringe on civil liberties, when judicial interpretation of the Constitution may be necessary, or during interactions with law enforcement where an individual's rights must be clearly understood and upheld, such as the right to an attorney outlined by the Miranda rights.
The questioning of legality is also pertinent when previous court decisions, or precedents, may affect the current interpretation of the law, as seen in the evolution from Plessey v. Ferguson to Brown v. Board of Education. Furthermore, a judge's conduct and the objectivity or potential bias in their decision-making process can also raise questions of legality and fairness in judicial proceedings.