Rather than something generic, here's a scenario with made-up numbers to better explain the goal:

Charging from 80% to 100% puts more strain on the battery than charging from 60% to 80%, even though it's an addition of 20% each time.

So let's say you use about 40% of your battery daily, and charge from 60% to 100% every day, and that drops your total capacity by 10% each year. You'll have 6 years before your battery won't last a whole day.

If instead that +40% charge was going between 40% and 80%, the reduced strain might mean you only lose 5% of the total capacity each year. That would get you 8 years before your battery won't last a whole day.

Getting your battery to last longer like this also means that a year or two in, if there's a day you expect to need the full capacity, you can just turn off the limit for that day and your battery will last longer than it would have if you never limited it.

charging the phone all the way up to 100% is less efficient than just charging it to say 80&, it's not linear. That reduction in efficiency creates heat, while your phone is also already working really hard navigating, playing music, blasting the screen at high brightness (assuming you're driving at daytime). All the heat can cause your phone to start performance throttling and could cause it to overheat and shut-down, but it will also hurt your batteries longevity

To extend the life of the battery. If you limit charging to ~ 80% it will get more charge cycles.

Lithium batteries degrade faster when very full or very empty. Samsung lets you limit to 85%.

Battery health in most cases