Succ() and Pred() would usually be used for enumerated values.

[pascal]
type
TSampleEnum = (seOne, seTwo, seThree);

var
Enum: TSampleEnum;
begin
Enum := seTwo;
Enum := Succ(Enum);
end;
[/pascal]
For the case you describe, Length(V) + 1 is definitely the more common usage.

As an aside, I read somewhere (I think it was on High Performance Delphi which is now gone), that
[pascal]
i := i + 1;
[/pascal]
is faster than
[pascal]
Inc(i);
[/pascal]
Mind you, I have not given this any serious testing, so it's just hearsay at the moment.