TSS, the why

[juju]

Simplest put, TSS gives you lots more pellets to fill in a pattern. TSS .410 can do what lead 12ga did.

With lead you have to choke extra tightly to get what few pellets you have into the core of the pattern. With TSS you have so many pellets that's going to happen without choking so tight.
There's lots more to be said on the subject, and I'm sure some will, but the great numbers of pellets are what you should understand first.

 

[Macintosh]

Whether thats a good thing depends on the use. Most of my bird hunting is at extremely close range—8-15 yards mostly, very rarely more than 20-25 yards. Even from a cylinder choke TSS simply patterns too tight for my taste, and I consider that a poorer performer than lead. For long range only shooting (turkey, lr waterfowl, etc), that may be a benefit.