As @alspal and @Aphrodite have said, use a Dictionary. Just load it from Local Storage when your game starts and save it only when needed, such as when changing level, exiting the options screen, game over screen etc.
I've just switched my project from WebStorage to LocalStorage just now. It seemed quite cumbersome until I've started using the Dictionary method and now it's nice and easy.
Async data loading is generally better because it doesn't freeze your game when loading and the standard for many other engines/coding languages (C#, Flash for example). I know most Construct games won't have loads of data to load but you also have to remember that one of the targets for Construct 2 games is the mobile market where the games won't perform as well as on PC and any bit of optimisation welcome.