Quote from joesan:
Thanks guys for your clarification.
Oldtrader, you mentioned T-bills. I have one further question about T-bills. Currently part of the money not used as margin exists as cash in my IB accounts. If I buy T-bills, will this bring me more interest gains than the interest that IB is paying to its customers.
A quick look shows T bills currently yielding:
1 month: 4.98
3 months: 4.88
6 months 4.96
So yes, if you account for the state/local tax exemption, T bills do yield slightly more than the 5.051% (beyond 100k) earned on USD at IB, but not much more except maybe for NYC & Yonkers residents.

but that's a list of top FCM's ranked by customer funds. I don't know if "most people" are shifting money back and forth but certainly others are doing as you.