Another assistantship application question

[mammatus]

 As I said in a post last week (thanks for the helpful responses!), I am applying for a bunch of assistantship positions. All of the positions have department-specific application forms with questions about why I want the position, relevant skills, etc. Each also requests a resume. Some of them ask for a cover letter, but most don't. For the ones that don't, do you think I should send one? I know in general cover letters are a definite, but I'm worried it will be a bit redundant since my answers on the application clearly address most of the stuff that usually goes in a cover letter (motivations for applying, transferrable skills, etc.). Suggestions?

Thank you so much!