Water Heaters - Teflon tape missed on compression fitting

I’m a newbie, but I just installed a new water heater today. I used the compression fittings with flex copper connections. When I installed the first compression connection, I forgot to put in the Teflon tape - doh. I was going to unscrew it and put it on, but I remember a friend from work telling me (way back when…), that the compression connection crimp the copper pipe and if you unscrew it – then it’s no good. You basically have to recut the pipe and install a new compression fitting. So, I let it go and did the other 3 connections with the Teflon tape. At first, it was leaking a little bit at the “no Teflon tape” connection, but after tightening it a little more – it’s ok now - no leaking. (Might be a coincidence that the other 3 didn’t have any leakages the first time – hmm...)
My question is: Should I go back and put the Teflon tape in? Or is the Teflon not that big of a deal (and it really was a coincidence)? Do I have to recut the pipe and install a new compression fitting? Or was he wrong and I can just unscrew, tape it and rescrew back on? I’m asking this not for the short term, but long term. I hate for it to one day leak and spill onto the electronic control sitting on top…that won’t be good. Also, it took me a while to figure out how to install this thing and I just want to do it right. Help.

tinman, Welcome to the DIY Forums.
I am a little lost on where you put the teflon tape on a compression fitting. If it had male iron pipe threads on one end of the fitting, and compression nut and ferrule on the other, you would use teflon on the threads that screw into another fitting. The compression part needs nothing on it. Compression fittings are made to be taken apart as many times as you need to. Most are found under sinks for connecting the supply tubes to the supply valves.

I see that a lot on DIY (teflon tape on compression). Like majakdragon indicated, it is not needed. The threads do not seal the connection. In fact, some plumbers will use a drop of oil on the threads to reduce binding and ease assembly.

Thanks guys. Good to know I don't need the teflon tape on the compression fittings and that I can unscrew and rescrew it without any worries. That put me at ease a lot. (FYI - It went down to the mid 20s last night and got into the 50s in the day and still no leaks)

Glad it worked for you.