You will find in every app review and How To guide will first explain if the app is a stand alone or sharing application.
You should think through what you would like your iPhone to be to you prior to making application purchases. When we say ‘stand alone’ or ‘sharing’ we are talking about the data you input into the aftermarket application you spent your money on.
Will you need to share information with others at work, in your household, in meetings? If you are creating or editing a document (text file, database, spreadsheet, calendar, ToDos, etc…) is it helpful to be able to share that item with others for their use and review.
Or, are you a silo with your iPhone/Touch? Keeping your own calendar, collecting and storing data only you will use.
The next item you will want to think about – are you going to create and manage only on your iPhone/Touch or do you want to edit those same files on your Mac and PC? Developers choose different methods to let you share information between your desktop and iPhone / Touch.
There are applications that sync their application back to a Web site (hosted by someone else… are they secure and will they be in business tomorrow?)
There are applications that sync to a Web site that then sync back to a desktop application. These are nice since you can edit offline on both the Desktop and iPhone / Touch then sync all together as Internet access is available.
There are also apps that sync their information directly to the Desktop application via a WiFi network. Which means that both the Desktop and iPhone / Touch have to be on the same network (easy at home) but will need setting changes on your notebook when mobile – creating a mini network of two.
For every app you find in the iTunes AppStore – there will be versions that are just for your personal device, tied to your computer or able to share with others. Think what is going to best suit your needs now so when you read reviews or look through the AppStore you will be able to buy what works the way you want you want your iPhone to work for you.