Well, not really.
How TTL Lighting Works
In a gist, TTL lighting is an acronym for through the lens metering. The way it works is essentially by the flash system reading the aperture setting and the ISO setting then figuring out from there how much power it should output. You can tell it to crank out more power or less power accordingly when you want or need.
Who Would Use TTL Lighting?
Fact: Professional photographers do what they need to in order to get the shot that they want or need. This even includes sometimes shooting in Program mode, aperture, and using TTL flash. Photographers that often used TTL flash metering are wedding photographers and photojournalists simply because they have to be able to capture candid moments. Sometimes sports and portrait shooters do this too but they also have to know and understand it isn’t always effective. So after a while of getting frustrated, they may switch to manual flash output in order to get the shot.
Myth: All professional photographers only shoot in manual for everything.
Truthfully, only some do, but they instead do whatever works for them and you should too.