There’s no sunsetting of global templates, only the ‘global elements’ feature that hardly anybody was using anyway.
You’ll still use templates for all posts/pages/archives views etc when building your sites and be using them all the time, the overall workflow will be very similar in that regard.
Only the Bricks team knows exactly what the components functionality will be in it’s entirety, we have only seen a brief preview of the early idea.
But from that preview… the main difference will be that if you use, say, a section with a bunch of elements in it… let’s say it’s a testimonial section with a slider that you need to use in different places. You’ll be able to save this whole section as a component and then reuse it in multiple templates or pages across your site. And then have control over either changing parts of it in one global place (where it changes everywhere across the site), or individually.
It’s not something I’d recommend holding up creating any sites with Bricks over, it’s not a complete change of workflow, just an extra ability to keep things more organised and maintainable as you’ll be able to create more reusable pieces that can be used in different contexts.