I saw many examples of code without these modifiers (in books, CPAN modules, documentation) and they are typed only when needed.

So I think - no, those are not good practice, rather those are just tools which I either need or not in my particular case.

Regarding 'm' switch, I use it rarely, every time I use it I clearly imagine on how my strings are constructed and why namely I want line beginning.
So it will be the first candidate to leave your list, IMO :):)