Quote from Miles Tinker, renowned for his landmark work, Legibility of Print, performed scientific studies on the legibility and readability of all-capital print. His findings were as follows:
All-capital print greatly retards speed of reading in comparison with lower-case type. Also, most readers judge all capitals to be less legible. Faster reading of the lower-case print is due to the characteristic word forms furnished by this type. This permits reading by word units, while all capitals tend to be read letter by letter. Furthermore, since all-capital printing takes at least one-third more space than lower case, more fixation pauses are required for reading the same amount of material. The use of all capitals should be dispensed with in every printing situation.
Suggested using sentence caps instead.