Is it wise to have one card for miscellaneous purchases?

I got 2 debit cards and 1 credit. Only one debit card is for miscellaneous, whatever purchases. I place fewer funds on that card and don't mind; let's call it card M. The other two cards, those I never give out over the phone nor online.

Yesterday I've used card M to buy a club trial over the phone for $20 a month. Card M is the only one I don't care too much though, as long as money is only charged from that card.

Is that wise though? To use 1 card for miscellaneous purchases?

Is it wise to have one card for miscellaneous purchases?
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