I've seen many job advertisements, where they specify work load, i.e. "Software developer 70-100%".

What does this actually mean and what does it say about the company?

Does it mean that one would be working anywhere from 70 to 100% of work load per each month, depending on how much he would be needed by employer, or that one would work some fixed rate, which is negotiable between 70 to 100%?

Is this a red flag? A way for start ups to decrease costs and squeeze the most out of employer?