Why it matters
A sharp tagline does years of repetition work: it frames what you do before anyone reads further and gives people the words to describe you to others. A vague one ("Excellence delivered") is wallpaper: worse than none, because it occupies the space a real message could hold.
How it works
Good taglines make a specific claim or promise a specific feeling, in your voice, in under seven-ish words. They come after positioning is settled: the tagline is the compression, and compressing mush yields mush. Test: could a competitor use it unchanged? Then it says nothing.
What to do about it
Write the one-sentence version of your promise first; compress only once it's true and specific. If you can't get under ten words without going generic, keep the sentence: clarity beats brevity.