T7 Exonuclease has even less activity on single stranded DNA than Lambda Exonuclease, acts at nicks unlike Lambda Exonuclease, and is less processive. Since it is less processive it may be more useful for unidirectional nested deletions. The enzyme can be diluted to control the reaction rate. With a highly processive enzyme, like Lambda Exonuclease, dilution gives a mix of completely digested products and undigested substrate.