If your organization uses person accounts,
you can convert leads to either person accounts or business accounts.
Leads with a blank Company field are converted to person accounts.
The default person account record type for your profile is applied to the new person account.
Note that you can only create leads with a blank Company field using the Force.com API. Leads with a value in the Company field are converted to business accounts. The default business account record type for your profile is applied to the new business account.
As a best practice, use different lead record types and page layouts to differentiate leads that will be converted to person accounts from those that will be converted to business accounts.
In particular, remove the Company field from the page layouts of leads(So that it can be blank) that will be converted to person accounts, and make the Company field required on the page layouts of leads that will be converted to business accounts.
