Many large companies have a bad debtor ledger comprising of various small and difficult debts for which they probably think it is no longer cost effective to chase.
However, your bad debt ledgers might contain £millions. They may have been written off in accountancy terms, but that does not mean that you should not try to recover money on them.
Alternatively, you may be carrying out a realisations project as part of a restructure, insolvency or factoring arrangement. Whatever the reason, realising the value of a debtor book has the potential to unlock a balance sheet asset and turn it into cash.