We employ a per-project model of engagement when the scope of work is defined and fixed. With a clear idea of the features and functionality of the product, along with the technology stack to be used to build it and the time-frame needed to deliver, it is possible to calculate the efforts and resources needed to complete the project.
When the scope of work, though defined at an initial level, is not fixed, and may change during the course of developing the product, or when the nature of the product is such that involves continual development and iterations, we employ this model of engagement. We fix the resources to be used for the project, who then work as per their given responsibilities on the product.
Choosing to employ the per-project model of engagement makes more sense when there is a clear picture of what the product will be. The set of features and functionality, the technology to be used to develop it, should be known to the client. This is usually the case when considerable research has been done to validate the product idea and details.
If the product is well defined, then a per-project model of engagement will help develop the most efficient product with economical costs and a set time frame.
The dedicated resources model of engagement should be preferred when the product’s final outcome and state are not defined before the commencement of the project. Product features and definition may evolve as the product is under development, and continuous iterations and revisions may be necessary before the ideal product can be delivered. In such cases, it makes more sense to allocate resources and their time based on the time frame of the final delivery.
With dedicated resources, a product with variable scope will turn out to be more economical and efficient, ensuring the best delivery without having to worry about recurring costs for optimizations and revisions.