The first way concepts can improve your code is by making it more generic. Do you remember the cases where you needed to change the container type in one place, which caused a cascade of changes in other places too? If you weren't changing the container to one with totally different semantics and that you had to use in a different way, that means your code may not have been generic enough.
On the other hand, have you ever written a template or sprinkled auto over your code and later wondered if your code would break if someone changed the underlying type?
Concepts are all about putting the right level of constraints onto the types you're operating on. They constrain what types your template can match, and are checked at compile time. For instance, let's say you write the following:
template<typename T>
void foo(T& t) {...}
Now, you can write the following instead:
void foo(std::swappable auto& t) {...}
Here, foo() must...
