What is the purpose of the cache? I am using a phone with limited internal memory, and I noticed that my app cache has swelled up to 130 MB. What are the pros and cons of deleting the cache for certain apps? I don't understand what the cache is used for in the first place. Could someone explain?
Cache:-Its a temporary storage file used by websites as well as the applications to store some data on your device.

Cache memory contains references(where to store the settings i.e. in which folder it should load or store the source file ), thumbnails(images to be displayed in the application) etc.

Advantages of Cache:-

1.Once you have already loaded the application then your application loads exceptionally fast when compared to the first time load.(Apps like browser will load your websites much faster as they are stored in your cache)

2.Instead of the application loading the wallpaper from the source(Phone memory) every time you load the application it will create a buffer memory from which it can directly load the wallpaper saving the processor of the phone from doing this task.

Disadvantages:-

1.The website takes some time to load the requested page as there's no buffer memory. This is not much big disadvantage as for the second time the page will load fast.

2.Although your pages are loading fast or the application is responding faster there is limited storage space which the Cache memory can store. Once it get's filled / is nearing to then other application/same application will get slow as there's no space for the application to operate.