Here is the scenario.
We have multiple business units using CRM. ABC account called into Company X for Product X. A lead was generated (lead source recorded in the lead), and converted into an account, contact and opportunity. Then, months later, ABC account calls in to Company Y about Product Y. They say they found us by search about Product Y. Most I've talked to say in that case you should simply create opportunity for product Y via the existing account. This kind of thing happens often for us.
However, this approach seems to significantly complicate the lead analysis process. If the first lead is a Lead, but the subsequent leads are actually Opportunities, you have to analyze the productivity of our lead sources across two different entities.
Also, how do you avoid double counting "leads?" You have to count your new Leads by lead source, but which opportunities do you count as leads? The ones without an originating lead? Seems complicated.
Almost seems easier to enter all subsequent leads as Leads, and then convert them to opportunities.