Apologies, I mean the Blaser Saddle Mount vs the Blaser Saddle Mount with Rings. I assume the Blaser Saddle mount does not require rings.
The Blaser Saddle Mount is either with rail or rings mounting option.
There are loads of advantages in a rail mount, as you do not have to worry about getting the crosshairs level with the bore, there is no pressure and stress on the scope, therefore no rings marks, and is 100% recoil proof.
So why have the ring mounts?
For scopes that don't have rails!
i thought the premium brands , swaros, zeiss, schmidt & b would all have rails, is this only on certain types. Am looking at a Z6i 3-18 x 50 BT. Thx
They will usually have the option of a 'bare' scope, (for ring mounting), or rail mount - you'll have to check with the manufacturer's websites or dealers/distributors to check which specific models the rail mount is available in.
In the example you've quoted above it is available with the 'Swarovski Rail' mount - check out the 'Product Variants' drop down menu and you'll see an 'SR' version:
http://uk.swarovskioptik.com/hunting/z6i-c20050107/z6-3-18x50-p-l-4a-300-p5006232
The Swarovski rail mount system is the best out there as it has teeth on the scope and teeth on the mount that lock into each other so it's impossible for the scope to move under recoil
(the Swarovski rail mount system is also used by Kahles and Meopta I believe)
the other brands s&b , Zeis etc all rely on tightness of the mounts to the rail they do not have teeth so even tho it's highly unlighkly there is a small chance they could move under recoil but very doubtful