That ("Load when X available") is what I do too, except it's not
In reality, I just use mass drivers for in-system mineral transport. Only for transporting minerals from one system to another do I use freighters, and when I'm doing that I usually just schedule the routes so that they never run empty. But in the old days before mass drivers "Load when X available" was the way to go.
That was the second time I'd seen the "slow down to save fuel idea" - just wanted to make sure that people reading it understood that going slow in and of itself doesn't save fuel on the trip; it's just a different (and less precise) way of doing "Load when X available".
John