pentejr: 13/8 adds a safe spare to 8. As grenv says that gives you the option of using a double, 1-1 being especially tasty. Even without a double you get to use one builder to make a home point and still have another for subsequent rolls. A piece on 8 is a banked asset in a way that slotting your opponent's barpoint isn't.

If that barpoint blot is hit then you've lost the entire roll unless you get one of the 14 retaliatory rolls. You mention thos 4/36 spoilers for that barpoint blot but there's also 5-1 which gets you double-tapped and in danger of a blitz. Then, not only do you waste the opening move but also your second roll too, unless you get a 1 or a double.

The split and bring-down-builders is the best move with many rolls because it advances your cause on both sides of the board. A setback in one of these areas isn't a total loss.

Splitting with a difference of 1 is relatively safer than other splits. A point made on the 2 is deep and commits two builders. Splitting with 2 is vulnerable to a 5-5 and a blitz. Splitting to the 4 and 5-points and getting pointed on is much more uncomfortable than the same on 2.

None of these things is conclusive but they all add their tuppence worth to the mix.