From the SB perspective, it accomplishes two things:
1. Establish that you are real and capable of providing sugar (even a small amount like $5). A lot of girls don't want to engage with a guy who doesn't use cashless transactions, and this shows them that you are capable of doing that and willing to engage in sugaring to make you worth their time to pursue you further.
2. A LOT of people have their real name associated with these types of accounts (Venmo, Paypal, Cash app, etc.) which gives them a great advantage in looking up more information about you. And we all know how little information we prefer to give them about ourselves and likewise find out about them.
I'm not suggesting these are good reasons for any of you to go ahead and engage them in this way. If you do, try to create your account with anonymous information that doesn't send any identifying information about yourself. I've only used Cash app with SBs I've had an established relationship with, and even then, only begrudgingly and in rare cases.
I haven't been too impressed with the numbers of newer and active SBs using the site, or the quality of the profiles (photos to what they say about themselves), so maybe there being fewer girls active the supply/demand is working in their favor? Just a theory.