Sea&Sea YS converter

Can anyone advise on the benefits of using the YS converter, and is it worth the money. Looking forward to hearing from you.Many thanks.

Assume you mean one like this:  https://www.seaandsea.jp/products/digital_slr/accessory/008.html

There are many types and brands of TTL converters available - wired and optical.  They are used either in place of the built in flash  or on cameras don't have a built in flash to trigger your strobes via either cable connection or optical fibre.  If using in place of built in flash they save batteries on the camera or on the case of cameras without built in flash are essential to trigger your flash..  There are many options and brands as mentioned, the right one to use depends on a number of things including if one is made for your model of camera and in some cases if there is enough room in the housing to fit the converter, 

SO in summary they are very useful but whether you need one or would benefit depends on your exact situation.

In my opinion, the TTL converters don't worth the money. They're expensive, and when you get into the habit of shooting in manual you ain't going to miss it. They're only reliable (and not always) in macro shooting. When shooting wide-angle no one of them are good.

I do fine with manual for macro photography, since I also usually drop to manual focus and use focus peaking to get exactly what I want in focus.  Nudibranchs are polite enough to stick around while I fiddle with my strobe knobs.

And with snoot work or black water dives, manual is your only option anyway.  A mispositioned snoot means TTL will dump a full-power flash (heating up the strobe), and black water is, well, black.

But shooting damsels and flasher wrasse is much easier with TTL.  The subject-to-camera distance can change very rapidly.  Or if I'm shooting blennies and I look up and a ray is swimming by, I can just take the shot with TTL.  Or if I'm in current, and I need one hand to keep position with a tickle stick.

Manual power means adjusting strobe power is a slower two-handed operation.  It's great if you can set up your camera and then wander around looking for the shot that fits your setup.  But not as good for spontaneous shots.