This capitalises every character in the input.
Where uppercase is genuinely required
Country and currency codes, some product identifiers, spreadsheet headers destined for a system that expects them capitalised, and legacy formats that specify uppercase fields.
Where it is a mistake
Body copy and headlines. Uppercase text is measurably slower to read because word shapes disappear, and in marketing contexts it reads as shouting.
The one-way problem
Uppercasing discards information. iPhone becomes IPHONE and no automatic process recovers the original. Keep the source text if you might need it back.
Try it: Convert Text to Uppercase on SeoWolf's Notepad.