When you have a line that’s over the line length limit, clang-format will need to insert one or more breaks somewhere. You can think of penalties as a way of discouraging certain line-breaking behavior. For instance, say you have:
Namespaces::Are::Pervasive::SomeReallyVerySuperDuperLongFunctionName(args);
// and the column limit is here: ^
Clang-format will probably format to look a little strange:
Namespaces::Are::Pervasive::SomeReallyVerySuperDuperLongFunctionName(
args);
You might decide that you’re willing to violate the line length by a character or two for cases like this, so you could steer that by setting the PenaltyExcessCharacter to a low number and PenaltyBreakBeforeFirstCallParameter to a higher number.
Personally, I really dislike when the return type is on its own line, so I set PenaltyReturnTypeOnItsOwnLine to an absurdly large number.
An aside, this system was inherited from Latex, which allows you to specify all kinds of penalties for line-breaking, pagination, and hyphenation.