In an engineering design process, this is usually the most creative part. It's fun to brainstorm new features that you could add into your product, system or service. And it's always a useful exercise to do because you might come up with ideas that are quick and easy to implement while adding value to your offering. Even so, there will always be features that would cost more to realise than they'd recover in increased revenue.
If it'll be prohibitively expensive to include every desired feature in your product, you need to prioritise.
Which features are essential because the product won't function without them? Which are highly desirable? And which can be added into future versions or premium editions of the product?
In marketing this is often where business owners find themselves overwhelmed.
Every business owner I've ever worked with can write a list as long as my arm of the marketing activities they could do if time and budget were unlimited. But how do you know which activities will pay off? How do you know in what order to do them all to get the best ROI?
An unprioritised wish-list is overwhelming and stressful.