When to take ignite or exhaust as a support
As many can see in the current high ranking games, supports have either been taking exhaust or ignite. Ignite can be taken as a support to increase kill pressure and lane and in late game teamfights, but gives the chance that one particular enemy that is fed to destroy the fight. So, taking ignite as a support summoner is a risk. Another case of taking ignite over exhaust is when the enemy teamcomp doesnt have the type of carries that suffer a lot from exhaust. For example: exhausting a fiora vs exhausting an orianna. Part of the reason support ignites in soloQ are not as prevalent is due to the soloQ factor of one particular enemy member getting fed, so exhaust would be more useful.
exhaust can give my adc a couple seconds of free damage time. ignite...not so much