Hi Kishen,
Plug-in and custom workflow activity required to be signed first before it can be deployed to CRM.
What is influence of signing you can refer below MSDN definition.
Assembly signing (also called strong-name signing) gives an application or component a unique identity that other software can use to identify and refer explicitly to it. A strong name consists of its simple text name, version number, culture information
(if provided), plus a public/private key pair. This information is stored in a key file; this can be a Personal Information Exchange (PFX) file or a certificate from the current user's Windows certificate store.
-http://msdn.microsoft.com/en-us/library/ms247123(v=vs.80).aspx
Thanks and regards,
Hiren Solanki.
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