The scenario is that (roughly) 90% of the hypergrowth-style startups which raise a first round will fail to achieve enough momentum to successfully raise a second. And due to the business model choices they've committed to, failing to raise at that point is equivalent to going out of business. A first raise is often too small to be able to do everything they'd like, so they suggest decide that it's in their best interest (long term) to forgo a salary where possible, in order to buy a few extra months of progress before you're forced to start shopping for investment again.
Of course, folks give advice based on their own experience, but it doesn't always generalise to folks in different situations, which is potentially why that would seem like silly advice in (what I assume is) your scenario.
(minor edits toward the end for clarification)