I think if you check T5 there's a huge emphasis on use of the reaction table. Not so with CT, I can't remember it ever being a factor in MT, and I haven't gone through the GT rules (only the supps) to voice an opinion. I'll assume it's in MgT.
It's present in CT...
Referenced in Bk2 starship encounters, Located in Bk3.
CT 81 B3 p.27:
Reaction throws are made upon initial encounter, and one throw determines the reaction of an entire group.
Reactions are used by the referee and by players as a guide to the probable actions of individuals. They determine responses to business offers or deals (admin or bribery expertise serves as a DM). Reactions govern the reliability and quality of hirelings and employees. Generally, they would re-roll reactions in the face of bad treatment or dangerous tasks.
CT 77 B3 p22-23 includes the same text and the same reaction table.
It's pretty explicit - so if i wasn't emphasized, either the Ref was rolling but not telling you, or houseruling it away, or substituting his own judgement in a situational case. Two of the three of which I've been known to do.
MT, it's part of the encounter flowchart, RM p 43, Encounters Step 11.
The whole process of modifying that initial reaction is an entire chapter: Interpersonal Tasks. The Reactions table is simplified to 4- Rude, 5-7 neutral, 8+ polite, but that's not enough to determine hostility nor cooperation; those come from tasks following.
It's useful, but it's not a straightjacket. Apply with common sense and GM mods ...