why is genre a relevant concept for audiences?- its relevant to audiences as they know what 'type' of thing they like and by seprating films into genres means thats audiences can pick and chose from exerience of what they like and what they dont like as they have a sort of pre-conseption of what the film will be like as seen before. 

How does genre effect film production companies?- genre effects them but in an extremely possitive way i think as it gives them a ready made tried and tested structure/recipe to follow and make there film by as they already know that it works; a sort of cheat sheet blue print. 

why is genre useful for film distribution companies?- its useful as they already have ready made fan and a target audience for each genre who are sure to come see a film if it is described to be a 'thriller' or a 'horror' etc...