The leads could loaded into Global workspace and routed to respective partitions by a triggered campaign.
Leads loaded drectly into a specific workspace may exist elsewhere. There is a risk of duplicates depending how the process is implemented or worse, the false impression leads are "disappearing" when they are loaded because they just update the record on a different partition.
I would reading the complete documentation to understand the interactions between workspaces and partitions.
It is safer to invest time to get it right first than reverting a bad setup later.
http://community.marketo.com/MarketoDeepDive?id=kA5500000008QMtCAM