It matters if you're have to move the final application to a client over a slow connection.
Writing a Swing app with a single panel and a couple of buttons that instantly blows up to a 20, 30, or 40MB jar file because of runtime dependencies may not "be heavyweight" but it certainly "feels heavy".
The basic question is whether or not the client runtime libraries have been "properly factored" to take this kind of limitation in to account. For example, WebLogic puts the kitchen sink in to their weblogic.jar, but they do have a much smaller "client.jar" file for standalone clients that want a smaller footprint.
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