I just gave a presentation at WordCamp Denver last weekend about integrating Gutenberg into themes. The Gutenberg experience is absolutely far better if your theme has integrated support for Gutenberg, including the new Wide and Full alignment.

Gutenberg itself provides basic support for most themes, but there are almost no existing production themes that support Gutenberg on both the front end and the back end, or Wide and Full alignment.

I've released a plugin that makes most existing themes compatible with Gutenberg called Theme Support for Gutenberg. I'd really recommend trying this plugin to see how Gutenberg works with Wide and Full alignment. In addition, for themes that currently support theme styling with TinyMCE, Theme Support for Gutenberg also provides near WYSIWYG to match the theme in the Editor.

Seeing theme integration with Gutenberg really changes the experience, and this plugin will let you see the potential for many existing themes. (It won't break how your theme works now - just likely improve the Gutenberg workflow.)

My free theme, Weaver Xtreme, also has complete support for Gutenberg if you want to see what real theme integration looks like.