Think about it this way. Although there isn't a 3 sided dice, for this example, just assume there is. You would expect to have a 1/3 chance of getting any one number on each roll. Every single roll, no matter how many times you roll, you should have a 33% chance of getting a 1, 33% of getting a 2, and 33% of getting a 3. That's random.
With the suggestion here, it blocks the last 1/2 of rolls from appearing again. What that means is that on roll 1, you have a 33% chance of each number. However, on roll 2 and on, you have a 0% chance of one of the numbers and the other two numbers have a 50% chance. That is not random.
Depending on the need of the script, that may be okay. However, if you need something that is truly random, then that is definitely not it. I would never suggest using such a "random" number for anything like dice or anything else that need to have the possibility of getting the same result multiple times in a row. Whether you believe it or not, it is possible to roll the same number on a 6-sided dice 10 times (or more) in a row. The odds are extremely low, but it is possible. That's what it means to be random. Perhaps some seeded random numbers are not as random as they could be, but that depends on how they are seeded. But they are still going to be more random than this.
