PKI software tokens (or soft tokens) can be used when you need a convenient method that is easy to rollout, but does not necessarily have the highest security level. Typical use cases include authentication at VPN access point and web services or for digital signature of emails and documents.
Software tokens are often used in combination with other methods. For example, a smart card might be required for Windows logon, but the security level of a software token is enough for VPN access.
Software tokens are delivered as PKCS#12 files or published in to Windows certificate store. A software token is used together with a password for authentication, signing and encryption.