I got what it does but what's the big deal of adding or dropping an index, I guess i'm not dealing with enough records it should make a difference to me
why would someone add an invisible index, its useless
Not sure what's not clear. When there is an index it makes a difference in the execution (most of the time to the better, but sometimes to worse if things are not done well), in a normal production environments with release cycles etc. you wouldn't want to change anything just because. Everything needs to be tested and benchmarked.
So someone can create an invisible index which doesn't affect query execution (except when specified) and do the testing, then switch in a sec to a visible index when ready. (The other way, when sunsetting an index, is even more simple.)