As I already told you about the Tally.Net, that will allow you to connect to your Company Data remotely over Internet Connection. Apart that Tally Solutions will be informing you about the updates made to the software and allows you to install the Latest Software Package to work.
If you have subscribed to Tally.Net Subscription you can use Login as Remote Tally.Net option in the Startup screen of the Tally.ERP 9 Software to access the Company Accounts available in different location by providing the Tally.Net User id or Password. If you have a Legal Software then can use the Login as Remote User option available in Company Info. menu.
Suppose I renewed my Tally.Net subscription on 1st day of September 2011 and installed Tally.ERP 9 Series A Release 4.31 but Latest Release 5.03 available, I wanted to upgrade my software with the Latest Release 5.03. My Tally.Net subscription already expired on 31st August 2012. As per the subscription I can only upgrade to Release launched upto that date i.e. upto Tally.Net subscription expiry date. The Releases launched after the 31st August 2012 (after expiry of Tally.Net subscription) will not be permissible for me to Reactivate my License in that release. Hence, I can only upgrade to Release 3.61 as it is launched on 17th August 2012 which is released before my subscription expiry date.
So, in order to get these services without interruption we need to subscribe to Tally.Net annually once. And this is what a Tally.Net subscription.