Let's talk about the ways of classifying the project rationales (not very serious).
1. To earn a money
There are projects with direct impact on revenue, profit, cost. For instance, a switching to a more productive technology, cutting expenses.
Outcome is estimated in money.
2. To mitigate some risks
The projects related to a better manageability or directly targeted to an identified risk.
Lower risks (probability * possible impact) should be the outcome of this kind of projects.
3. To gain more loyalty
The projects about customer's loyalty. I believe that quality perceived by customer also converts to loyalty. That's why quality projects (making a service faster, stronger, better and customer journey easier) fall into this category in my opinion.
Value can be measured in NPS and churn decline.
4. For passion and pleasure
Outcome can not be measured. You are engaged, maybe, to someone else's loyalty project (type 3). But, anyway, probably, these are the most valuable projects.