I have had carp while the marker float is still in the swim after feeling around and baiting up to it, and had takes within minutes of reeling in.
I tend to lead around, or even use the marker float every trip. Sometimes a feature is so 'tight' that I need to be hitting it, a metre either side could see my bait in missing the gravel bar totally, or in a thick weedbed.
Right now I'm using the leading around to find fishable spots, and then get my rods clipped up to that length, with far bank markers as my aiming point. Just casting out 'blind' could, again, see my bait in thick weed. I don't mind my freebies landing in weed, but it is soul destroying reeling in a ball of weed with your hook point masked in weed, and the contents of the PVA bag stuck in the middle of it.
I may know the features of the lake, even mapped it out, but a marker float, and/or leading around are invaluable every trip. Some trips, I may actually cast and bait up to the marker every day.