Lets make an example of Risk=Reward on Halo 3.
Lets imagine you are playing a game of FFA Slayer on Snowbound and there’s someone in the ghost. You have no way to kill him from spawn, since frags aren’t very effective against ghosts and your AR & Pistol don’t even scratch vehicles.
You now have several choices:
A) Get the Spartan Laser(this is the riskiest approach, but has the biggest payoff)
B) Get Sticky Grenades(this is less risky, but it will be harder to deal with the ghost than it would be with the laser)
C) Get a Plasma Pistol(this is even less risky, but it will be harder to hit the ghost and board it than it would be to stick it or laser it)
D) Stay in the bases and the tunnels to avoid the ghost(this carries no risk, but confines you to interior spaces, there’s no risk so there’s no reward)
Less Risk=Less Reward and More Risk=More Reward
The risks are that another player or the guy in the ghost will kill you. The risk increases with the amount of time you would be exposed, as you are further away from the laser than you are the stickies and further away from the stickies than you are the Plasma Pistol.
Now lets make an example of the same scenario on Halo 4.
While there is currently no FFA playlist (Regicide doesn’t count) lets just imagine there is.
So you are in a game of FFA Slayer on Complex and there’s someone in one of the ghosts. You can easily retaliate from spawn, and have a fairly good chance of killing him, since you can start with a Plasma Pistol and stickies and your primary weapon can do a fair bit of damage to him, you could try to earn an ordnance drop, but that doesn’t include much risk either.
The only risk you are taking is confronting the ghost and him killing you, this is already present in Halo 3, but there is further risk because you have to earn the tools to destroy the ghost in Halo 3.
This could also be applied to BTB, in Halo 3, the BR couldn’t kill someone from half-way across the map on Valhalla, if you wanted a kill you had to move in and risk being killed. In Halo 4, you can just fire at him with the DMR, if you start to lose, just pop into cover, no risk.