Nowadays, I'm reconsidering my workflow and I'm curious about if the most experienced real estate photographers are using one catalog in LR for each shoot or if all the shoots are included in the same catalog (every one in its folder, of course!)
I think you'll find that most low volume photographers that have everything in one catalog but some that break their photos down into smaller catalogs.
Scott Kelby the, Lightroom author, claims that in the early versions of Lightroom processing use to be slower with large catalogues but with the latest versions of Lightroom processing doesn't slow down noticeably with large catalogs. However, I've noticed that with large catalogues backing up the catalogue up and moving it takes much longer.
I think it comes down to your personal organisation preferences. There are pros and cons to both having everything in once catalogue and having a catalogue for each shoot. The video above from SLR Lounge gives a more in depth explanation:
One catalog for everything
A Catalog for each shoot
So my recommendation would be for most photographers is to use a single catalogue but for very high volume photographers use a multi-catalogue workflow.