Given the loss of exposure latitude with the transition from film to digital we need to use every tool we have to help use in difficult lighting settings. Flash Fill although it has been around for decades is one such tool.
It seems very odd to use flash in the sun but if you are within your cameras flash range if can create a completely different image from the classic available light photograph. I recommend you get in the habit of taking one additional shot with flash on! It only takes seconds and it only costs you a little energy. One this becomes second nature you will be amazed in the new category of images you can make.
Many very difficult lighting situations can and will be solved with flash fill.
If you are about to hire a Wedding or Event photographer for a once in a lifetime moment ask them ” Do you like to use available light or do you use flash?” If they saw “Oh I only use available light!”, do not hire them! If they say “I prefer available light but in some situations I need to use flash fill”, you have a viable candidate.