Many people may think kart scales aren't needed in karting, but most of those are the ones not racing really competitively. Like it or not, you need to be able to weigh your kart and position weight where you need it to be.
Before things got advanced in karting, most racers would just use "bathroom scales" bought from retail stores. Really though, these get the job done, and aren't that far off. Of course when your working in percentages and close racing, you want it to be exact.
That's where digital sets come in. They can be pricey but you can't beat a good set up that is extremely precise and comes with its own own box that you can hook all four into and get the read outs and percentages on the spot without doing the calculations yourself.
Once you make the leap to digital scales like this, you will notice how different it is if you ever go without them again.
Of course with anything, the digital sets keep getting more and more advanced. The more money you want to spend the more things it can do for you. Mainly what the upgrades are for are improvements in how data is handled and stored.
These are pretty neat. It's a platform that holds your scales that you can adjust to always make level. This is a big thing for guys how like scaling at the race track, like when they go for weekend long race trips. If your going to spend the money on one of these, it would make sense to have digital scales along with it.
You can always build your own stand to hold the scales if you prefer. A lot of people find it easier just to purchase one.