That's the whole point!

If you're not sure - don't mess with it!

And if you take the risk, then it's one in two.

A group of giants means they're guarding something tasty; surely you can scrounge up 2500 for an extra scout hero to check whether it's there or not. But having to report to your opponent afterward how many times you did it and whether you broke the rules is not the most pleasant task.
The other extreme - you deliberately left a stack of weak neutrals somewhere to split, but they had a Guard of the Sands (GS), you used them several times, so now should I have to techport?
By the way, the probability seems to be less than 0.5 - people once investigated the presence of GS on an XL map, they never found a pattern, but the matrix was always quite sparse.