Section 3.3.2 Long Ledgers

Even though ledgers are finite, they grow over time and can become unwieldy without careful management.

Optimized Sequence
As the years progressed and Parliament passed more and more decrees, Paxons had to pore over an ever longer list of decrees to find the current olive tax or what color goat could be sold. A legislator who returned to the Chamber after an extended voyage had to do quite a bit of copying to bring his ledger up to date. Eventually, the legislators were forced to convert their ledgers from lists of decrees into law books that contained only the current state of the law and the number of the last decree whose passage was reflected in that state.
LAMPORT, P. 17 — §3.3.2

Lamport is describing what we now call a snapshot. Instead of keeping the full ledger indefinitely, a node can record the current state of the system along with the last applied decree. Snapshots drastically reduce storage requirements and speed up recovery and replication in distributed systems.