Well, you need internet to download the actual tool, unless you do that from your device. It's also helpful to have the instructions open, which you would need an internet connection for.
Just a quick note to keep an eye on this forum post if you have HBOOT 1.15 or 1.19 for a NO DOWNGRADE S-OFF: http://forum.xda-developers.com/showthread.php?p=33471597
Also if you are having problems getting S-OFF for HBOOT 1.12 please know that Support for our tools is via IRC channel #juopunutbear on freenode ONLY. If you do not have an IRC client you can use this link.
We DO NOT provide support, instructions, or downloads via XDA. Please see our website: http://unlimited.io
Using how-to guides, "kits" and using other instructions on XDA to S-OFF your device is not recommended and will not be supported by Team Unlimited. If you want the best experience and results - go direct to the source. Dealing with support issues through the forums is inefficient and posts may get lost in long support threads, of which we would have too many to actively monitor. We have therefore decided that all support should be through our IRC channel. This will allow us to help you in real-time and through the whole process.