Back in 2018 when I scoured the internet for agents and started my first spreadsheet to that end, I found sites
like this one. I think this is what she means.
I assumed that these newer agents would have a higher request rate and such, but in practice I found that their form rejections tended, not always, to be a little more clumsy and they often (like 20% of the time) left agenting within the year anyway (it's a high-turnover profession.) Some of these were writers/authors as well, which is fine, but it shifted my view of 'who goes into agenting.' It felt like some were trying it as a means to charge their own writing ambitions. Again, fine.
Over the few years since then, I've continued to gather resources and whatnot, and for example, have found that some agents in Pitch Wars showcases will request entry after entry after entry, using the same language in each invitation to submit. Again, this is fine, and they are busy, and I might well do the same, but it shifted my view of their jobs a little bit. ("Oh, they're using a blanket form request. Hmm, how do I feel about that?") In contrast, some established agents might go onto the Pitchwars showcase and select a handful of entries and tailor their invitation to each. This observation might mean nothing and is generalities anyway.
When Pitchwars ended, some of the chatter from newer agents was how frustrating it was to find a gem and offer representation only to have a writer use that offer to leverage something with a top-tier agent who might not have participated in the showcase at all. These frustrated newer agents said how draining Pitchwars was for them, because they never landed the writer they courted, in the end.
I followed up on one writer from Pitchwars (she wrote a historical novel I considered briefly for a comp, and her showcase entry had an unreal number of requests) and I saw that in the end her representation is an agent who did not even participate in Pitchwars. I mean, good for her for watching out for her career--I'd do the same--but you do start to realize how the agents in the showcase might have felt about that.
So, I think what the note to you meant was to say that some agents are more likely to be scrambling around for clients and Writers Digest is a place to find them, like
this site. I have found that going through QueryTracker and looking at request rates is more helpful. Most agents in SFF request under 3% or so of subs. A high percentage of SFF agents request 0%. (Perhaps they only work on referral or something.) But some agents request 5-10% or higher, and those are more likely to be agents looking for clients.
Separately. For what it's worth, in the sciences, there is similar advice to graduate students: Work with a top tier professor with tenure, and you get X. Work with a newly hired professor and get Y. Neither choice is better or worse. It's simply advice.
Last thing, one of my full requests in 2018 came from an agent starting her own agency... so perhaps she was 'hungry' in this way.