You can see the blur in the volleyball even with strobes being used due to the 1/250 sync limitation.

TTL Flash offers some advantages over manual flash. I use the Nikon speedlight system that has helped me have an edge over many other photographers not using the system.

There are three things that make me choose my Nikon Speedlights over the manual flash: 1) I have no sync speed limitations, 2) quick—I don’t have to pause to take readings and then set the camera, and 3) I can shoot at very wide opening f/stops.

You can see the blur of the basketball due to slow shutter speed with the strobes.

When you can shoot at any shutter speed then you open the possibilities for so many things.

 
1. You can shoot at high shutter speed like 1/2000 or 1/8000 of second to stop the action.  You see when the shutter is open at 1/250 sec for manual flash there is enough movement is sports to have some motion blur.  You see this is hockey and basketball.

 

2. You can control the background—outside! You can crank that shutter speed up and underexpose the background by say 2 or 3 stops and then up you flash output 2 or 3 stops to properly expose a subject, yet underexpose the background.  Great to get those dark blue skies behind a subject.

The TTL flash easily figured the correct amount of fill flash on the fly here.

You don’t always have time in some situations to take the time to take flash readings and then set the camera.  News events are a good example where you need to be ready.  Recently I photographed the founder, president and son of the president for an article.  These folks are known to change their mind at the last second and ask you to photograph them just about anywhere—this is when having a TTL portable flash let’s you adjust on the fly.

Taking a flash into the rain forest where coffee is grown in the mountains of Mexico lets me pull it out under all the shade to make the photo look like sunlight.

Many photographers today are shooting with an f/1.4 lens.  If you go outside to shoot you cannot use a manual flash because shooting at f/1.4 means you will have to shoot at a very high shutter speed.  The TTL high-speed sync lets you shoot with a flash. 

To be able to shoot large groups outside you need those high f/stops that will often require the manual flash.  To be flexible and use high sync shutter speed you need the TTL system.  What I hope you now know is there are advantages to both systems.  Don’t buy both systems right away.  Buy one and learn how to use all the advantages of the system.  Once you find you cannot deliver photography to clients because the system you have is limited—buy the next system and learn all it can do.