Answer:  Most likely you don't.

However, if you fall into any of the below categories, an 80+ inch television may just be a viable and appropriate solution for you.  If not, well, picking up an admittedly excessively large television still carries all of the bragging rights and show-off potential that you would imagine it to have.

Reason 1: A large living room.
This just makes perfect sense.  If you have a very large distance between your television set and your couch, even the best 55-inch TV will seem microscopic.  Sure, most average people can't afford a house in which this is the case, nor would this be a preferred design for those who can afford such space, but just in case that's what you're working with, here is an 80 inch solution.

Reason 2: Home theater
Maybe you don't have a large living room, but a dedicated theater.  You're probably accustomed to utilizing a projector unit, but what if you want to take advantage of all of the new technology found in television sets these days?  An 80 inch, or larger, television makes perfect sense in this situation.

Reason 3: Video game or sports immersion
Are you a major gamer or a sports fanatic?  If your passion is either of these things, there is no way to get closer to the game.  For the times that you can't make it out to the stadium, and for the times that you become frustrated that it is impossible to ever walk into a video game, super large televisions seem to at least numb some of the pain.

Reason 4: Business meetings
Board rooms, conference rooms, control centers and situation rooms. The larger the screen, the better in these scenarios.  Pack a bunch of over-important people into a small room, and you'll quickly want to have a large screen to keep them thoroughly engaged with whatever remedial information you've been tasked with presenting to them.  Look at the bright side, if you are delivering bad news, at least you can play something flashy and hope they become distracted.

Reason 5: Public display
Restaurants, bars, clubs, airports, shopping centers... the list goes on and on.  I really don't think anyone will ever have to convince you of the fact that no TV can ever be "too large" as long as I remind you of how futile it could be to try to check arrival and departure times at an airport in the 1990s.  Without smartphones and mobile Internet, you were forced to huddle around measly 20-something inch televisions mounted overhead and still quint to make out the fuzzy fonts.  Good riddance to that.