In early development environments, the transaction log is quickly filled by creating, dropping, and re-creating stored procedures and triggers and checking integrity constraints. Recovery of data may be less important than ensuring that there is adequate space on database devices.
with truncate_only allows you to truncate the transaction log without making a backup copy:
dump transaction database_name with truncate_only
After you run dump transaction with truncate_only, you must dump the database before you can run a routine log dump.