More BS from John, not helping, and diluting and polluting the forum. The OP question was on RedGard when used to waterproof a shower and the use of reinforcement fabric. They specify it in some circumstances, and wouldn't if it didn't help make a reliable install. If you do not use it, it probably will fail over time, but you might be lucky. Few things in life are cast in stone, except that sometime, you will die. Nobody is going to say it will absolutely fail, just like some people get away without using thinset underneath cbu on a floor, but eventually, it usually does fail.
Since the OP asked about Redgard, and actually spelled it correctly, my thought was that they had a clue about the actual product they were asking about...not whether I thought it was the best for their job. Redgard works if you apply it properly, it's just not my favorite product. The manufacturers have a vested interest in your project working, and to do that, you must follow their installation instructions.