Magento2 – Before Place Order in Onepage Checkout

Why you try to do this way for changing text?

You can do this simply by translation.

Create a i18n/en_US.csv inside your theme

OR

Inside your module create i18n/en_US.csv, In that case make sure your module load after Magento_Checkout module. So module.xml looks like:

<?xml version="1.0"?>
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
    <module name="Vendor_Module" setup_version="2.0.0">
        <sequence>
            <module name="Magento_Checkout"/>
        </sequence>
    </module>
</config>

Your csv content should be

"Place Order","Do you like Place Order?"

Clear all cache.

XML Checkout. Should think about XML first.

1) A standard practice

Most of the developer will take a look the XML first to check the XML layout.

2) Maintenance

If you're familiar with checkout XML, you will see that it's easy to change. On the other hand, LayoutProcessor::process() will be "messy" if there are one more changes from different extensions.

When do we need to use LayoutProcessor::process() plugin?

1) Complex logic

It's hard to say in this case. But for example:

\Magento\Checkout\Block\Checkout\LayoutProcessor::process($jsLayout)

......
['payment']['children'] = $this->processPaymentChildrenComponents(
                $jsLayout['components']['checkout']['children']['steps']['children']['billing-step']['children']
                ['payment']['children'],
                $elements
            );
......

We need to assign the billing info to each payment. As we can see, it's impossible to use XML.

2) Remove component completely

We can use XML to disable a component, but component still is rendered. We can remove this component completely.

XML:

<item name="%the_component_to_be_disabled%" xsi:type="array">
    <item name="config" xsi:type="array">
        <item name="componentDisabled" xsi:type="boolean">true</item>
    </item>
</item>

LayoutProcessor::process()

unset($jsLayout['components']['checkout']['children']['steps'][%path_to_target_node%]); //%path_to_target_node% is the path to the component's node in checkout_index_index.xml
return $jsLayout;

3) Can do what XML cannot do...

Don't need to explain more here.