The cells in the right column of the table shown in figure 4.5 have different leading or padding. Observe that the default leading of the content of a cell in text mode is equal to the font size. Internally, the leading is set like this: This is different from the default leading of a Phrase object outside a PdfPCell.
There can be a lot of differences between a UDF and stored procedure, as the prior link has shown. Another difference is the UDF can be directly selected from, whereas a stored procedure requires one to insert the results into a tempory table or table variable.
Like procedure v. function. Expressions have a value, while statements do not. I don't think I ever made the connection between the difference between statement v. expression & Pascal's procedure v. function difference. (Which I thought was a useful distinction.