I am trying to understand the purpose of DNAses in eukaryotic cells. I think that they are present as antiviral software to destroy single stranded DNA that is floating around in the cytosol and nucleus. However, DNA is single stranded in the nucleus during replication and transcription but those are not touched or few are degraded. Does DNAse have any other functions in eukaryotic cells that I am missing? Thanks.

Depends on the eukaryote, but in most multicellular ones the role is more of a regulatory and cell-cycle-dependent nature. Examples include involvement in apoptosis, modulating autoimmune response.