I suppose it depends on your goals. But for myself, and for many others on this forum, one of our goals is having a steady supply of sexual encounters, more or less whenever we want, on our own preferred frequency. It's just really hard to achieve that with only one SB. No matter how great she is, there will be times when she's not available and you are, and vice versa. And of course there's her monthly period to consider.
If you want a consistent schedule of let's say 2 dates per week, that's very difficult to achieve with just one SB. And as we all acknowledge, sugar arrangements take time to establish and don't last forever. So a serially monogamous SD is going to have long dry spells after each arrangement ends while he works to create a new one.
This all argues for creating a "rotation", ie, multiple sugar babies at any given time, all of whom you see on some sort of schedule. All the while, you'll be browsing on SA developing new arrangements, hopefully at the same speed as your attrition rate to keep things even. Your rotation might be as few as 2, or many more than that, depending on your desires and abilities.
Finally, there's a real emotional risk involved when you have only one SB. I was down to one exclusive sugar arrangement for a year during the worst part of the pandemic. I became very emotionally dependent on her, much more so than I even realized. So when she dumped me and ghosted, very suddenly with zero warning, it hit me very hard. I had no one to turn to and it took a long while to create a new rotation starting from scratch. For all these reasons I prefer to date several SBs at the same time.