Why can warrants be used in some cases but not in others?

This is how the question is stated in my assignment. What does it mean? I know you need to get a warrant for searches and you must mave proable cause or the judge will not give you one. But what does it mean that warrants CAN be used in some cases but NOT in others?Why can warrants be used in some cases but not in others?
There are is cetain criteria met in order to use such warrants. For example: You have an arrest warrant for John Doe, who happens to be at a party at his friend's house. You cannot use the arrest warrant to make the arrest in the friend's house. You might be able to convince a judge to sign off on a search warrant for the friend's house to get John.





Another Example: Say you have a search warrant for Farmer Bob's house because you think he is growing marijuana. You get to his house and you see he has a big barn. Can you search it? Not unless the warrant includes the structure.Why can warrants be used in some cases but not in others?
Bloomberg for President 08'


SIGN THIS PETITION


www.draftbloomberg.com
There are many types of warrants


Arrest


Search


There are other types - not as common





Arrest warrants are for criminal acts. Search warrants are for persons, premises, vehicles, etc.