The reason the company names and contact details of unopened Leads are hidden from the Partner is so that he or she has to actually click and view the details ("open" the Lead) -- once a Lead has been opened all the details are always visible.
Hiding the details for unopened Leads allows you to accurately track which ones have been viewed. If you have a lazy Partner that never opens Leads, you can then re-assign those Leads to a different Partner without worrying that the first Partner has the contact info and you have two Partners pursuing the same Lead.
FAQs
Can I disable the setting that hides the details?
No.