It's supposed to give a sense of urgency, to make the reader feel he/she's on the spot. I hate it and now check carefully before buying.
I read some of Patricial Cornwell's books years ago and enjoyed them but I gather she's fallen by the wayside and now writes in the present tense.
The worst are those written in the first person in the present tense.
I recently bought a French novel, a detective story set in Brittany, and thoroughly enjoyed it. So I bought the next 2 in the series without looking at the contents. Blow me if they aren't both written in the present tense, so I shan't be buying any more of that writer.
