Every admission to the US is subject to CBP inspection. In general, as long as you are using the B2 for trips of modest lengths of time, and spending more time outside of the US than inside, it won't be a problem.
"Overstaying" would be if you stay beyond the allowed time given by CBP at entry. The date that you are allowed to stay until for any given visit is found on your I-94, an electronic record of admission to the US.