We carry two anchors aboard Roam, an R-25. The primary is the claw anchor sold as a factory option. It has worked very well for us. The secondary is a 13-pound Danforth that is stored in the compartment below the V-berth and above the bow thruster. It has six feet of chain and 150 feet of line.
I can think of three reasons for cruisers to carry a second anchor.
The first is if you lose your primary. Anchors sometimes get caught under a log or rock and cannot be retrieved. There are lots of articles about how to retrieve a stuck anchor, and I won't repeat the information here other than to say that, on rare occasion, anchors cannot be retrieved. Using a trip line may reduce the probability even further, but again there is no guarantee. Some newer anchor designs incorporate features that allow them to be pulled from the opposite direction and often free themselves.
The second reason to carry a second anchor is for extra holding strength if you are expecting high winds. You can set the anchors out in a "V" pattern and the load will be distributed between the two. It can be difficult to retrieve them if the boat swings and the rodes wrap around each other, but you will probably sleep better. The best sleep can be obtained by using a cell phone app such as Drag Queen. It senses it the boat is moving and will wake you if it moves more than a preset distance.
The third reason to carry a second anchor is for tight anchorages where you don't have room to swing. Often the current switches in these areas. Set a bow anchor and let out twice as much scope as you need. Drop the stern anchor and then center the boat between the two anchors. Make sure to give the stern anchor a good tug to set it as well.
So, there's a long answer to a short question. If you're planning to do any serious cruising, get a second anchor. One anchor is probably OK for most lunch stops and perhaps an occasional overnight in good conditions.
Rich