Full Idea
In a tableau system no sequent is established until the final step of the proof, when the last branch closes, and until then we are simply exploring a hypothesis.
Gist of Idea
In a tableau proof no sequence is established until the final branch is closed; hypotheses are explored
Source
David Bostock (Intermediate Logic [1997], 7.3)
Book Reference
Bostock,David: 'Intermediate Logic' [OUP 1997], p.283
A Reaction
This compares sharply with a sequence calculus, where every single step is a conclusive proof of something. So use tableaux for exploring proofs, and then sequence calculi for writing them up?