What T does
T returns the supplied value if it is text, and returns an empty text string if it is not. It is mostly a compatibility function, but it can still be useful when you need a formula to pass through text only.
Practical examples
Keep text values and ignore numbers
=T(A2)
If A2 contains text, T returns that text. If A2 contains a number, T returns an empty string.
Pull only the text part of a mixed range
=T(A4)
This is a simple way to strip out logical or numeric values when a downstream formula expects text only.
Common mistakes and notes
Empty text is still a text result
For non-text input, T returns "", not a blank cell and not zero.
T is mostly for compatibility
Microsoft notes that Excel already converts values automatically in many situations, so T is not needed in most modern formulas.