The buff that can lead to victory or defeat and what they do. Why they are important and what are the best times to obtain them?
Side objectives can help you win the game if done properly but can easily cost you a team fight or/and the side objective you are trying to get. The "dragon","Herald/Baron" is a side objective that you may/will need help killing because they do so much damage and have lots of "hp"(health points). The "dragon" and the "baron" buff benefit the team even if a teammate does not help kill the monster. Monster level up depending on the highest levels of the players in that game making it stronger over time.
Dragon comes up at 3:00 minutes in the game and re-spawns every 6:00, dragon does not give out gold for killing it but it does give out a permanent buffs all game to the team that kills it. Dragons buffs can stack up, the buffs last all game and the elder dragon buff last 2:00 minutes or till you die. The amount your team kills the dragon will be the amount of dragon buff you will receive, example: if you kill the first dragon but the opponent team kills the next dragon and you kill the third dragon you will have the two first buffs that the dragon gives you.
Herald is right where baron is and comes up at 6:00 minutes in the game and does not respawn, Herald gives out gold, and the a buff spawns in the front of it. Only one player can pick up herald buff and it last all game. Herald dies by itself at 19:45 to give its place to baron that spawns at 20:00, baron re-spawns ever 7:00 minutes and gives out gold/buff to the team at kills it. If your team kills baron and you are dead then you will not receive the gold/buff, the baron is the hardest monster in summoner's rift to kill and takes team work to kill it.
This objective will give you an edge that may help you win the game and is important for you to get as many advantages as possible to have a successful game. The best time for doing this objective is when the other team is dead or not around, make sure you have vision around the area for the monster you are killing to see the opponent team coming before they get to you. If you can catch out the opponent jungler or a key player, then killing one of these monsters may be the right move because the other team will be out numbered and have a hard time contesting you.
Note: Baron is really strong and if you take to long to kill it the other team may be able to kill you and the baron, making for a huge lose and may cost you the game. Only do baron if you are sure you can kill it fast and the other team will not have the chance to steal it or kill you.