We have a checking and savings account at a traditional bank (for regular expenses and and a small emergency fund).
Then, at an online bank, we have about 9 separate accounts: Large emergency fund, tax account for estimated taxes, a holding account before funds are swept off to a brokerage, and a bunch of accounts for targeted savings (car, insurance, clothes, large purchases, home repairs, property taxes, and a few others. It's just easier to keep the funds segregated, and it doesn't cost anything.