One of the problems you’ll soon run into when building a block for Gutenberg is that as a block becomes more complex, storing its complete output statically becomes undesirable. If a block contains several fields or its output contains HTML markup, you don’t want to find yourself in a situation where this output needs to be changed at some point in the future and you need to retrospectively apply changes to stored block output in every post.
Gutenberg supports dynamic block rendering so that you can perform more complex output rendering on the fly, without having to store the complete output when the block is saved. This is the same method that shortcodes in WordPress use and allows you to move away from static block output. If you’re building a block for Gutenberg that uses anything more than very simple output, you should consider using dynamic rendering.