Map requirements
As you work on collecting requirements, an important step that you'll go through is to map the requirement to Dynamics 365 app capabilities. This task is different than you would do with a custom software or Microsoft Power Platform-only project where prebuilt business process logic doesn't exist as it does in Dynamics 365 apps. For example, Microsoft Dynamics 365 Sales has already implemented tracking sales opportunities, so you don't need to build that logic. Your mapping effort is to review each requirement and consider how you'll implement it. The mapping will commonly result in one of the following categories applying to the requirement:
Out-of-the-box - The Dynamics 365 app has this requirement built in and needs to be enabled or minimal configuration. Sales opportunities tracking is a good example of this category.
Configuration - The Dynamics 365 app doesn't support configuration by default, but by adding a few columns to tables or a few custom tables and maybe some automation, you can implement the requirement. For example, the requirement might be to track a commission amount on each opportunity. You could implement this requirement with some low code/no code configuration and perhaps some automation to automate the calculations.
Custom - The Dynamics 365 app doesn't support customization, but you could accomplish it by including some code developer resources to build a custom component or logic. For example, a code developer on your team could create a Microsoft Power Apps Component Framework control to implement a custom product configurator on the opportunity form.
Partner solution - Many partner solutions work with Dynamics 365 apps. For example, a product configurator could come from a partner solution instead of custom building.
These examples are categories that you can use, but teams aren't limited to these categories.
When combined with the level of effort and priority, you can use these categories to complete a fit-gap analysis. A fit-gap analysis is a process of evaluating how good of a fit that a solution might be for the problem that's being solved. In the preceding categories, out-of-the-box capabilities would be considered a "fit." This aspect is important in a business application like Dynamics 365 because it means that you fit what the app does. If you have a low "fit" percentage, then that app might not be a good starting point for building the solution.
Typically, requirements that end up in heavy configuration or custom categories should be examined to determine if options are available for moving them more in line with the out-of-the-box capabilities, with some configuration to match the unique requirements. It isn't uncommon for requirements to initially map to custom because a customer thinks it must be done as it was in the old system without realizing that Dynamics 365 differs slightly in its out-of-the-box support. Working with your customer to negotiate these types of requirements toward out-of-the-box capabilities can be beneficial.
Another benefit of the mapping exercise is to evaluate the feasibility of a requirement. Common reasons why requirements aren't feasible include:
A minimal number of people will use the feature.
The feature isn't technically possible.
Regulations or laws prohibit the feature or process.
Considering how a requirement will be implemented also has the benefit of identifying where you might need a proof-of-concept solution to identify how it will be implemented. Proof-of concepts typically involve building or creating an example of how a problem might be solved. It doesn't have the functionality of a production-ready feature, but it has enough to evaluate if the concept works. This concept can also apply to evaluating partner solutions to determine if they would solve the problem. Microsoft AppSource is a good place to find these partner solutions.
Regardless of whether you perform the mapping informally or formally as part of your project methodology, refining your requirements and understanding more about the level of effort that's needed to implement them can be a valuable exercise.