Vitally means 'in a way that really matters' — it makes the word after it stronger. In practice it lives almost entirely in one phrase: vitally important. That partnership is so tight that if you learn only 'vitally important', you have learnt about ninety per cent of how this word is used.

You will also meet vitally necessary, and, more rarely, things like 'vitally interested in the outcome'. Beyond those, it starts to sound odd. You cannot say 'he vitally helped us'.

It is a notch up from 'very important' and a notch more formal. You hear it in speeches, reports, editorials, and from a manager explaining why a deadline cannot slip. Between friends, people just say 'really important'.

The force behind the word is 'life' — vital things are the ones you cannot live without. So 'vitally important' carries a faint sense of 'we would not survive without this'. That is why it sounds too big when the thing is small, and why using it for everything wears it out.