Is semi untethered jailbreak worth it?

I have an iPhone 4S. I'm debating whether or not to do it. What features will I lose before I boot tethered? If I use redsn0w will it be easy to use evasi0n for untethered later on?

There's 3 diffrent kinds of tethering.

Tethered- it is jailbroken, but if you install a tweak and need to reboot, it dies, or it crashes. Then you will need a computer to turn it back on.

Semi Tethered- jailbroken. But if it you install a tweak and you have to reboot, it dies, or it crashes, you CAN turn it back on. However if you turn it on without a computer then the iphone will be in safe mode, meaning that it will act temporerally act not jailbroken until you can connect it to a computer and reboot it with the jailbreak.

Untethered- its jailbroken of course, and if it dies, it crashes, or you install a tweak and you have to reboot. You can do it with the ipod on its own and you don't need a computer for anything. (this is the one you should propobly want)

i would say just google up "untethered jailbreak firmware x.x.x" (x.x.x being your firmware) and you will probobly find the software for the untethered version.

Depending on what iOS your iPhone 4S is, I would use evasi0n as you mentioned. It is untethered for iOS 6.0 - 6.1.2. I don't believe there's an untethered jailbreak for iOS 6.1.3 yet. In my opinion, I don't think tethered/semi-untethered jailbreak is worth it. In the incident that your phone dies, you're basically screwed unless you have a computer/laptop. But that's just me.