When it comes to a new system, you always want to make sure you have all the accessories you'll need and possibly even get some accessories that maybe aren't needed but improve the quality of life. The latter is where the Charging Grip fits. The Charging Grip isn't necessary but it has the potential to improve the overall experience.
The problem with it though is is outside of letting you charge your Joycons, it doesn't do anything else special. To add to that, Switch comes with basic grip already and the Joycons last about 20 hours on a single charge. Furthermore, unless you're playing exclusively on the TV and don't own a Pro controller, have a second person who actively plays with you, and/or can't remember to attach the Joycons onto the system, it's usefulness goes down significantly.
I personally use the Switch portable half the time, I have a Pro controller, and I keep the Joycons attached unless I have somebody else over that wants to play, so this has been a pretty useless purchase for me. Maybe down the road I'll get more use from it, but, so far, I can't recall charging my Joycons using this. A word to the wise would be stick with grip that comes with the system unless you have a second pair of Joycons.