In one D&D campaign I played years ago, we had to roll our stats with the usual "roll 4D6 and drop lowest" rule, however with a special exception, that is, if all four dice had the same result, you got to keep them all.
So for example rolling 5, 5, 5, 5 would net you a 20 while a 5, 5, 5, 6 would be a 16.
What is the average advantage this rolling scheme would have given us?
Best Answer
The advantage in general is pretty low since the chance of that happening is small. The chance of rolling 4 identical numbers on d6s is \$\frac{6}{6^4} = \frac{1}{216} \approx 0.46\%\$. That would make the expected value of the roll rise by \$\frac{3.5}{216}\approx0.016\$ attribute points.
The more important effect is that there is an actual possibility of starting with a 24 in an attribute (or more with a racial bonus). Also there is no chance of starting with a 3. Whether this is something you want is up to you.