yes, this is a good question....
if you need to store only 10/50 values for example (health, coins, levels..) you can use the database...
but I'm thinking how I can store the array... for example, minecraft has a very big map where the cubes are stored on a JSON file or something like that...
If I like to make a world map like terraria (2d game) with the tilemap, it's really hard to load and store everything... I means, if the tilemap is 1000x1000 and the tile are 24x24 (so much data...) and the player can edit the single tile (destroy, building...etc) and you have 100 tilemap... every tilemap need 1 JSON file... the problem of save this kind of data, is if someone delete the cache of the computer (there are a lot of software to clean all of the data, or a lot of people do manually) you will lost all of the progress...
and to store on the database will be impossible... (for the tilemaps)
so, I'm thinking about to upload the single file, and when the player save, construct2 just upload the file in a specific folder and overwrite the older...
this is possible... if in the game you make a sort of registration for the user (when a person make a new user, one script in php make a new folder in your server with a name of the user) and when you open your tilemap from the layout (or from external JSON on the website) construct2 can check if exsist the file in a specific folder of the user... if exsist just load this file, if doesn't exisist, load the original...
doesn't exist a plugin for construct2 to make a sort of uploader and connect in your server (I think is very important to have a plugin like that) but is possible to make everything in php or java and just use AJAX request...I think this method would be the best to store the savegame
for example, I don't know how construct2 can upload the file JSON (you need to know where construct2 save the data on the local store...but maybe you need the permission of the computer...) but is possible to send with AJAX the array in a single string (crazy I know, the limit of the url is like 2500 characters...) and make a specific script to overwrite the file...