The technology plan is centred on the value proposition you have. It describes what you'll deliver as a product or service.
You might have an idea that requires to overcome a technical challenge and in this case the technology plan will be crucial and at the centre of your project. The technology plan will be a guideline throughout long development phases and the many issues to sort out one after the other. Keep your head above the water and get ready for an exciting journey.
But no all projects have involve technology, in some entreprises it'll just describe an existing product or service.
Anyways, the product or service you're selling will always have to be defined and designed. These specifications need to appear in your plan as you'll be communicating on them in order to build your value proposition. They can evolve throughout the duration of your project all changes need to be reflected regularily in your plan with accuracy to avoid issues.