As long as you don't try to change the indentation level within a block, it's allowed. It is, however, a style frowned upon -- you should be consistent and use

As long as you don't try to change the indentation level within a block, it's allowed. It is, however, a style frowned upon -- you should be consistent and use always the same ammount of indentation for blocks. There are a few styles regarding multiline statements though.