Brand ambassadors do play a role in enhancing brand image and bringing relevancy to a particular target audience.
If we take the Bond example mentioned by
@Hubert , Omega strongly associated itself with an icon.
While not everyone is a 007 fan, today, the link is rock-solid.
Not the case with Tag Heuer.
Their ambassadors are all over the place; models, musicians, athletes, pseudo-artists and what have you.
Even us, the hardcore brand followers are lost and confused.
Longines is a similar case of ambassadors bonanza.
Let's also have a look at IWC, and Bell&Ross.
These two are strongly associated with aviation through their pilot watches.
I believe they did a better job with Mercedes-Petronas and Renault than TH with Redbull.
They did not dilute the sponsorship, and stand strongly behind it. Even the timepieces produced for the occasion are part of their top tiers offering.