Savings accounts are a lucrative and relatively sticky offering. Many higher-rate savings accounts offer two (or more) tiers of interest, with higher rates applying to months where the customer does not withdraw or otherwise move money out of the account.[ß] The incentives mean that the customer is encouraged to deposit money INTO the savings account, but not take it out. If you don't have a full banking license, all that money is float - and you can invest it accordingly. Your net is the spread.

If you do have a full banking license, you can then use some of that sticky float for loans and earn a bigger spread. From what I have learned, small short-term business loans tend to be particularly lucrative, because the default rates can be impressively low. Big banks don't typically want to deal with those types of loans because the absolute ROI is simply lost in the noise and overall they do not move the needle enough to make a difference.

ß: you get access to better deals with less limitations if you have enough money to qualify for premier (or better) banking. The threshold is approximately the amount where the bank's wealth management unit becomes interested in you. I've told my bank that my absolute ceiling for any ongoing management fees is 25 bps and will manage my personal retirement funds accordingly. As a result they don't bother me, and I simply keep my fraction of investments at that bank in sufficiently low-cost instruments. I'm happy to pay my ongoing, sufficiently low management fees to them for this privilege.