Banks do not care, amex perhaps being the only exception here, that too only for new card accounts. I have done that for years now with NO consequence !!
It's simple, the more you spend, the more they earn from MDR ! One of the things which actually can flag your account is manufactured spending for rewards, milestone benefits etc over a period of time which make the banks loose money instead of making money from you ! Another thing that can flag an account is business spends on personal cards, other than that banks really do not care.