Copying a row out of a spreadsheet gives you tab-separated values on one line. This converts each tab into a line break, turning that row into a vertical list.
Why tabs specifically
Tab is what spreadsheets use when data crosses the clipboard. Copy a range from Excel or Google Sheets, paste it anywhere that is not a spreadsheet, and tabs are what you get.
The usual need
A tool expects one value per line. The spreadsheet supplies one row of many columns. This converts between the two without a round trip through another application.
Rows versus columns
Copying a column already produces one value per line and needs no conversion. This is for the case where the values arrived side by side.
Try it: Convert Tab-Separated Text to Lines on SeoWolf's Notepad.