Update Readme.

components/server-side-render/README.md

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 ServerSideRender
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-ServerSideRender component is used for server-side rendering preview in Gutenberg editor, specifically for dynamic blocks. Server-side rendering in a block's `edit` function should be limited for blocks which are heavily dependent on (existing) PHP rendering logic that is heavily intertwined with data, such as when there are no endpoints available.
+ServerSideRender component is used for server-side rendering preview in Gutenberg editor, specifically for dynamic blocks. Server-side rendering in a block's `edit` function should be mostly limited for blocks which are heavily dependent on (existing) PHP rendering logic that is heavily intertwined with data, such as when there are no endpoints available.
+
+Usage of ServerSideRender component could also be justified in the following two cases:
+* Lack of potential to take some existing widget-like functionality and improve its user-facing editing experience.
+* Unwillingness to create a full JS experience for a block considered legacy.
+
+Note that ServerSideRender should be regarded as a fallback.
 
 New blocks should be built in conjunction with any necessary REST API endpoints so that JavaScript can be used for rendering client-side in the `edit` function for the best user experience, instead of relying on using the PHP `render_callback`. The logic necessary for rendering should be included in the endpoint so that both the client-side JS and server-side PHP logic should require a mininal amount of differences.