Debit cards do have some interesting quirks (I don't use credit and you really can't use cash for everything), for example some hotels will get authorization for a significantly higher amount than the room charge to cover incidentals. If you use a debit card, that extra cash can be unavailable for quite a while (days to weeks). That can add up, a few weeks ago I had a $1000+ discrepancy between my "balance" and "available balance" for about a week (I spend about 1/3 of my life in hotels).

You also can't really trust that your actual balance agrees with what the automated phone/computer tells you it is, my 16 year old learned that lesson by running up about $130 in overdraft charges on her debit card in one day.