If it is B2 with multiple entries, generally speaking there is no issues with frequent visits however frequent visits with longer stays, say up to 6 months, may attract more scrutiny from the CBP at port of entry. In such cases, you may be denied entry or get issued with shorter validity I-94.
Also it is not advisable to extend B2 beyond 6 months of stay unless there is a compelling reason such as health issues that hinder travel.
Not to forget the IRS rule for substantial presence test that makes one treat as resident for US tax purpose and may be obligated to file a tax return, even if on B2 visa.