2^15 is equal to 32,768, the largest amount of text an Excel cell can hold.
the ROW(INDIRECT part is so that you can create an array in the exact amount of characters in the cell.
So, if the length of your cell was 10 characters, it would create a an array of {1,2,3,4,5,6,7,8,9,10} by iterating through those ROW values.
Now if the value was found at 8. This would be 3rd from the end, but the length of the string (10) - where it found the character 8 is 2, so you have to add 1 to show that is 3rd from the end.
However, your question now isn't what I was answering. You specifically asked about Matthew Brummel Smith and then your question changed. If you are trying to remove text before or after a specific character the answer would be different, so it's important to ask the actual question you are concerned about.
It sound like now, you would like everything before the last slash in a cell, if that's the case, then try this: