Conceptual differences
| Lead | Deal | 
|---|---|
| Potential customers expressing interest. | Genuine leads with formalized and structured engagement | 
| Preliminary opportunities in the early stages | Ongoing transactions tracked through defined pipeline stages | 
| Help organize prospects before qualification | Include a business value target and are tracked until they are won or lost | 
Differences in features
| Feature | Lead | Deal | 
|---|---|---|
| Can be archived | Yes | No | 
| Can be added to a pipeline / stage | No | Yes | 
| Can have a value | No | Yes | 
| Can be associated to a product | No | Yes | 
| Can be created through webforms | Yes | No | 
| Can be created using spreadsheet import | Yes | No | 
When to Create a Lead vs a Deal:
Create a lead when identifying potential interest for early-stage prospect management and convert it to a deal when a structured engagement is established, signifying a commitment to pursue the ongoing transaction.
Converting a lead to a deal will move all the interactions from the lead to the deal so that no information or captured communication is lost. So when in doubt, create a lead. You can either archive them if they didn't materialize, or you can convert them to a deal when you think your customer is expressing genuine interest in availing your service.
If you are certain that a customer is genuinely interested, then create a deal directly.