Enjoying beer is as easy as opening a can or bottle and taking a sip. However, you'll be robbing yourself of the pleasing sensory elements of a brew by not pouring it in a glass.
Since a whopping 80% of flavor comes from our perception of aroma, much of beer's aromatic expression, such as malt or piney hop character, is presented in the head, or foam cap.
When you don't pour beer into a glass, you can't experience that smell. Plus, you also won't be able to perceive the look of the beer, which is an important part of the experience.
Moreover, texture and mouthfeel are a major part of enjoying any drink, and it's tougher to appreciate the qualities of a liquid if you drink it straight from the can or bottle.