Despite what most people say, flash is not ALWAYS necessary, we need to destroy the belief that it is. Most of the time junglers are not in danger when they're in the middle of farming. Taking a summoner spell that won't be used half the time until mid - late game is inefficient. What can ghost do? It can make things more efficient and help you reach camps much faster, not to mention it's just as efficient as flash when you're ganking.
Jbels3 votesThe belief will die when it is no longer true
Joxcab1 votesYou realize it's for ganks when people Flash away and Ghost doesn't catch up fast enough because any amount of time longer than instant is too long, or you want to Flash-engage to kill them before they can react?
Hallbuster1 votesYou realize it's for ganks when people Flash away and Ghost doesn't catch up fast enough because any amount of time longer than instant is too long, or you want to Flash-engage to kill them before they can react?
There is that.....
Haihefa1 votesstart the ghost before you get there, due to ramp up time. Then when they flash your double movement MIGHT catch them.
archerno11 votesWhat if u need to flash for baron/drake steal?
Hallbuster1 votesWhat if u need to flash for baron/drake steal?
The chance of that happening is too slim, although still possible.
Frightning1 votesNo one uses summoner spells while farming, the use them in fights with other champions. In that arena, on the vast majority of champions, flash has been demonstrated to be superior (there are a handful of champions that are known for sometimes taking Ghost, such as 
and 
). Why is flash better?: The movement is instant, and especially because it can cross over walls.
CØulrophobia1 votesI take ghost on noctusrne and hecarim. nobody else really needs it.
MrHaZeYo1 votesMore so depends on the synergy to the champ.
Olaf, Hec, Rammus can use the Ghost's MS and uptime to gank better, while Elise, Lee, and Gragas need the flash to make their combo's more deadly or efficient.
Flashing also allows for instant catch up, baron/dragon steals, and escaping.
Hallbuster1 votesMore so depends on the synergy to the champ.
Olaf, Hec, Rammus can use the Ghost's MS and uptime to gank better, while Elise, Lee, and Gragas need the flash to make their combo's more deadly or efficient.
Flashing also allows for instant catch up, baron/dragon steals, and escaping.
So champions with speed boosts in their abilities should rely more on ghost?
MrHaZeYo1 votesIt's more so the question, how does Flash help me, or how does Ghost help me that it outweighs Flash?
Rammus usually takes Flash, I just like ghost on him cause it has a higher uptime for me to activate it once I know for sure I'm going to gank and I just come speeding up. I'm tanky enough later on that not having flash won't always mean the death of me. Although the change to his Q kinda sucks as it will stop it instead of just CC you in it now. Flash on him his good to tho to like flash the minion wave to get on top of them to taunt em.
Hec gets damage from MS, so it just makes him stronger in general, he also has his ult to act as a flash if he needs to. Similar to Shyv.
Ghost is better for sticking to the enemy, but is generally better on champs who will build some tank.
Flash is better on burst champions and squishys. a Flash Elise cocoon, or Lee sin Q flash R, or Gragas Eflash, are just to good of combos to give up for Ghost.
Hallbuster1 votesIt's more so the question, how does Flash help me, or how does Ghost help me that it outweighs Flash?
Rammus usually takes Flash, I just like ghost on him cause it has a higher uptime for me to activate it once I know for sure I'm going to gank and I just come speeding up. I'm tanky enough later on that not having flash won't always mean the death of me. Although the change to his Q kinda sucks as it will stop it instead of just CC you in it now. Flash on him his good to tho to like flash the minion wave to get on top of them to taunt em.
Hec gets damage from MS, so it just makes him stronger in general, he also has his ult to act as a flash if he needs to. Similar to Shyv.
Ghost is better for sticking to the enemy, but is generally better on champs who will build some tank.
Flash is better on burst champions and squishys. a Flash Elise cocoon, or Lee sin Q flash R, or Gragas Eflash, are just to good of combos to give up for Ghost.
Good analysis.
MrHaZeYo1 votesThxs.
Keep in mind, we don't do things because we want to, we do things because we feel we have to. I don't take flash because I want it every game, I take it because if I don't i'm hindering myself.
ThatEkko1 votesJunglers that need flash for there combo's/ganks. 
(Optional) 
Probably a few others i missed.