Should I Add Leads in Bigin?

Should I Add Leads in Bigin?

ok, first off I'm new here. I just started using Bigin.

I'm debating if it's appropriate to enter leads. by leads I mean a list of contacts that I have not yet reached out to...it's a cold calling list. 
if I enter them I can track them (I understand I'd have to import each as a Deal and then as  company (B2B)). Not sure if this will clutter up my CRM by having this. The alternative is track these unqualified leads in a spreadsheet until they have been qualified. 
Any insight or thoughts would be great.  Looking forward to your responses.