Setting a headline in capitals feels emphatic. In a search result or an ad, it usually performs worse than the same words in normal case.
Reading slows down
Readers recognise words partly by their outline — ascenders and descenders give each word a distinctive shape. Uppercase flattens every word into an identical rectangle, forcing letter-by-letter reading. In a results page scanned in a second or two, that difference matters.
Platforms may reject it
Most major ad platforms prohibit excessive capitalisation in headlines and will disapprove the ad. An uppercase headline can simply fail to run.
Where emphasis actually comes from
Specificity outperforms volume. A concrete number, a named outcome or a clear differentiator earns attention that capital letters do not. Save uppercase for short labels where it is a formatting convention rather than an attempt at emphasis.
Try it: Convert Text to Uppercase on SeoWolf's Notepad.