To use an on-line system you will need to have a permanent, stable Internet connection. Even on the PC based system you will need to have Internet to send sms’s from the system.
The advantages of going on-line are that you can log in to your system from anywhere and with any smart device such as a PC, tablet or cell phone.
There is much more security on an on-line system as there is no need to keep backing up your data, which needs to be done on a PC, based system. In addition with the on-line system, if your computer is stolen or it crashes, you can immediately be up and running simply by using another device.