The original handguard was triangle-shaped, composite plastic, and fairly short compared to many modern-day examples. It was there to protect your hand from the heat of the barrel and to protect the gas tube from external threats. Handguards have come a long way since the first AR-15. There have been some interesting improvements in the world of handguards since so long ago. If you want the classic look you can still get those as well, there are plenty of drop-in handguards available. 
     Currently, free-floating handguards are probably the most prevalent type. They are called free-floating due to being connected to your upper receiver by one point only, and not touching the barrel at all. They do everything the original handguards did with the added benefits of allowing more air circulation and not causing barrel warp. Barrel warp is where your barrel is not allowed to bend naturally because it is being hindered by the material it’s embedded in. Barrel warp will very slightly change the direction of the round being fired, as the barrel is very slightly not pointing in the direction you want it to. This very slightly affects accuracy. Whether you’re skilled enough for it to matter probably won’t stop you from getting one. 
     Some free-floating handguards have so much personality. There are many passionate beliefs residing in the hearts of everyone. A handguard can be a great place to express the things that ring true. From the ancient Molon Labe, which is an elegant and sophisticated way of saying ‘You can have them when you pry them from my cold dead fingers,’ to “We the people,” a reminder of a time when people were brave enough to stand up to the tyranny of an oppressive government, back when the weapons a private citizen possessed weren’t dismally outmatched by whatever the common military had. Or the ‘Don’t tread on me.’ which is kind of a combination of those two other sentiments. Then there is a handguard that looks like spartan swords and though cool enough by itself, it is part of a complete spartan AR rifle that has some other impressive features as well. There are also handguards that are beautifully crafted with flowers, insects, and even unicorns, all in positive and negative space. That is to say pictures with plenty of holes in them, for aesthetic reasons as well as to allow heat from the barrel to dissipate into the wind. If you are looking for a way to make your AR pop, you can’t do much better than any one of these. 
     They are often made of 6061-T6 aluminum, which is certainly strong enough for the demands placed onto them. This type of aluminum is also easier to work with and modify, so you can do a lot more with a handguard of this type. Luckily the two most commonly used types of aluminum aren’t conducive to shearing and you can readily use a 6061 handguard with a 7075 upper receiver. 
     Many of these free-floating handguards have the added benefit of being able to hang accessories all over them. Most have a Picatinny rail and either Keymod or M-Lok slots. With these you can put on your choice of optics including iron sights to co-witness or just use as a backup. You can also put a handle on it, especially if it’s got the Picatinny rail on the bottom or the 6 o’clock position. 
     The question of how much and where you want your Picatinny, Key-Mod, or M-Lok systems are important, and there are many differing versions of the answer by many different manufacturers. To save on weight a lot are deciding on having only partial Picatinny rails that are strategically placed, or no Picatinny rails at least initially. Keep in mind you can add partial rails anywhere your Keymod or M-Lok systems are. Depending on your set up this can save you weight. 
     Although there are a few people out there who have decided not to use a handguard (for whatever reason), with all of the choices available these days, not to mention the utility, there is no reason not to have one. Decide what kind of accessories you want on your AR (M-Lok, KeyMod, Picatinny), then let your personality decide. Find the one that best suits your needs, wallet, and artistic leanings and go for it.