Both manual and TTL flash options have unique sets of benefits and drawbacks. However, the majority of the flashes can be shot using manual method. But, TTL mode is compatible with only some flashes.
To use TTL mode, the camera hot shoe and flash must have a special set of pins. These pins transfer information. When it comes to an aspect like photojournalism and events like weddings and sports, TTL can be the prominent option. When you need to mix ambient with natural light, TTL can be a huge plus; it doesn’t require you to meter.
Manual light is more appealing in situations like portraiture, headshots, editorial and fine art photography. Manual flash output requires the photographer to take some time and setup the scene. However, it gives a better control over the light as opposed to TTL. TTL, on the other hand, determines the amount of flash automatically without the photographer’s consent. Manual flash works perfectly with large light modifiers.