To learn about the best that Hollywood and world cinema have to offer.
To know what directors and producers are looking for. Often they will reference classic or older films in writing, producing or simply communicating their new ideas in a way others will understand.
To understand directions when they are given to you. Film references are common with many directors and casting directors.
To borrow with respect and homage when it is appropriate to do so.
To know and and understand the industry you are a part of, fan of or interested in.
Over 125 years of movie history are there to study.
Study the comic timing and physical comedy of Harold Lloyd, Buster Keaton, Charlie Chaplin to the Three Stooges and Dick Van Dyke, from the broad yet warm comedy of Lucy to the over the top fast patter of the Marx Brothers, Jackie Chan to Ben Stiller, Tracy Ullman to Robin Williams.
Learn from to the dramatic flair of Marlon Brando to Lord Laurence Olivier, Kenneth Branagh to Sean Penn, Benedict Cumberbatch to Denzel Washington, Ray Liotta to Anthony Hopikns, and the tones of Orson Wells, Vincent Price, Samuel L. Jackson and Morgan Freeman the styles, skills and craft used should be studied, practiced, imitated and internalised.
Know Cinéma vérité and other film techniques so you can adapt to what is needed for each style. Know when to be large and when to be subtle, when to be natural and when to be a characature, how to use your voice, diction, articulations, dialects, accents, affects, and how to use these tools without making it obvious.
Above all, study how the greats come across natural, appeal to or become hated by audiences and how the actor contributes to a suspension of disbelief needed for the story to become real or entertaining for the audience.
I cannot make you do it. But appreciation of old movies is key to understanding how our craft becomes the story, and learning what works and does not work on film.
Start with the AFI Top 100 films, or build you won filmography to study, enjoy and apply to your craft.