The "glitch" is one that allows you to group a batters eye prop with a regular prop, and then be able to move that grouped prop anywhere on the field, including on the field of play. You can also then copy that grouped prop, and by then ungrouping the combined prop, have multiple copies of the batters eye prop. What it basically does is turn the batters eye props into normal props.
A great many designers have taken this option to make some really nice stadiums, designed to nicely replicate actual stadiums, or to produce some visually spectacular stadiums.
Personally, I opted not to use it because I figured SDS would soon disable the glitch and I didn't want my stadiums suddenly rendered unusable. In hindsight, I wish now I had leveraged the option. But, now it appears that SDS has decided to retain it.
Is this a sign that SDS is starting to listen? I don't know, but I sure hope so! Lord knows SDS has received a ton of very well considered and constructive feedback that if accepted would make Stadium Creator vastly better and more capable than it currently is.
Last point: to leverage this option, you have to first download from the vault one of the Batters Eye Glitch stadiums, as those are the only ones with the code "glitch" that allows you to do this special stuff.