Here's about the only things I completely rely on with the chartplotter. I use the speed over ground display to determine when I've actually come to a halt to drop the anchor. Not that critical, but nice. I also leave the anchor alarm on for 15 or 20 mins to see if we set. That has alerted me to dragging when I'm distracted by other things. Still, I would have figured it out on my own in time, just nice to have. I also confess that I take its word for time to waypoint and/or VMG, but only for cruise approximations, not specific dead reckoning navigation.
Now, as far as simultaneous navigation to a chart, its fantastic. It just needs to be cross referenced.