This is good.  You can also get the same effect by using partials in your erb templates.

This way you could do the following:
```
post '/' do
  erb: results, locals: { books: books }

post '/add' do
  erb: added, locals: { books: books }
```

Then you could include a different hardcoded message in each of your erb templates. I can't see any advantage of one over the other in this case.