It depends on the depth of the fish, wind conditions, and boat traffic in the area. If it's nice and calm, and the fish are around 4' or deeper, by all means, toss out a couple of anchors and keep adjusting them till you're sitting right on top of them. If it's a bit breezy, I'll use the trolling motor and move back and forth over the area. Boat traffic is the worst while trying to anchor and not get moved off of a spot, you have to have your anchors far enough away from your boat to allow you to cinch them up every now and then for adjustments you need. Too much boat traffic makes it almost impossible to fish while anchored. I have sat over many brushpiles that had about a 2' hotspot under the boat. You get 3" away from it and no hits at all, stick it back to the hotspot and nothing but fast action. I am sure others have found this to be true as well.
I would suggest a couple of anchors 10lbs or better. The smaller ones don't do much on a windy day. I carry 2-20lb and one 5lb in my rig. I have been known to create a three way support of anchors to tie my boat off just to stay over a particular spot. Good Luck!