Or it can be useful in an enemy system, as it is faster to put into action than a planet with a supply base.
Oleg, yes it can be a nightmare if you do want to prevent any waste. But why not forgetting about this waste? I won't even mention what will happen when you have ten systems for instance, and other "toys".
I am myself in love with this option, but I am a lazy player when it comes to micromanagement.
And even expansion in other systems is so much easier with this option, as you can colonize these worlds much faster than with Starlines, although you could also use both options.