Pros: Readability. Unique closing reserved words on compound statements will enhance readability and flexibility of a language. When an endwhile or an endif in a program is written by someone else, it is vivid which block is ending. Using braces is much harder is sometimes much harder to read.
Cons: Writability. They have the disadvantage of writability and thus, complicating the language by increasing the number of keywords. Use of more of these reserved words mean less words available for the programmer.