There are two dimensions of legal authority to keep in mind when conducting legal research.
Primary vs. Secondary
Mandatory vs. Persuasive
Is all primary legal authority also mandatory legal authority?
No: For example, Texas state laws are primary legal authority but they're only mandatory authority in Texas. Sometimes primary legal authority can be used as persuasive authority to effect a change in law or policy or influence how a court interprets a law. For example, an 8th Circuit Court opinion is not mandatory authority in other circuits, but it may be used as persuasive authority in another circuit (or lower) court attempting to rule on similar facts. What other examples can you think of?
Why does it matter?
The more authoritative weight a source has, the better support it provides for your argument.
If legislative history sources are only persuasive authority, aren't they all the same?
No, some legislative history documents are more authoritative than others. From least authority to most authority, they are (1) the text of the bill (all versions) (2) committee hearings (3) House and Senate floor debates (4) Committee reports
If Committee Reports are the most authoritative, why don't I just find those and be done with it?
All parts of the legislative history work together. You may find important and helpful information to support your position in all of these sources. For example, comparing changes to the text of a bill over time may be insightful, even if only speculative. Also, because committee hearings include statements and testimonies from both supporters of the legislation and parties who oppose the legislation, you get a glimpse of opposing positions and can account for those in your own work.