Do I really need to use leads?

Do I really need to use leads?

Hello!
We just signed up for Zoho and are starting to work on customization.

We sell to a very specific target market and I was thinking of not using the Leads portal but rather have a drop down menu for contacts to differentiate if they are a Target, Lead or Customer.

What are the benefits of using a different module/database?

For some of our customers, even if they do buy, I still want to continue to market to them like the rest of the targets/leads so what is the point of having them separate?

Would really appreciate some help in deciding if it is worth separating.

One point I just thought of...Opportunities can only be created from a contact and not a lead. And so I convert someone, create an opportunity, but we don't get the project. I want them to still be a Lead so I can continue to market to them.

Am I missing something?