Just like any tool, strobe is the right tool in some situations. Its primary TACTICAL purpose is to disorient. This works a lot of times if used correctly, and just incites a charge to "Turn it off" in others.
If disorientation is not the tool needed, then the strobe is not the right tool at that time.
Its secondary purpose is to attract attention - and, if a rapidly flashing light will attract the attention you want, then strobe is the right tool, and so forth.
The RATE of the flashing effects seem to imply a certain urgency, so a fast strobe is seen as most urgent, and a slow flash is considered more beacon-like, and is even called a beacon on some lights that flash slowly.
I've never used SOS...and if stranded somewhere where there may be other lights, and needed to attract help...I could see it as an option.
I think if I was in a dark area, such as the woods or ocean, etc...and people might be searching for me...ANY light would attract attention. If the light was flashing in a beacon pattern, at least the light would last longer/have an extended run time...and SOS would count in that regard.
As for whether its a hidden mode, or readily available, that really comes down to your use of the light.
LEO/Tactical people want the lights to always come on in HIGH, and, to have strobe as a one touch option.....they do NOT want to scroll through modes to brighten the light, or find strobe.
Pretty much Everyone ELSE want the lights to come on at the LOWEST setting they think they'll need...and then to be able to be brightened if needed. This is one reason why "Tactical Lights" are accidentally purchased by non-tactical people, who just thought a "Tactical Light" would be a better light...and then are annoyed by it having strobe which they normally HATE, coming on too bright to read the map, etc.
A "tactical" UI is optimized (If its actually meant to be used "tactically")...for one set of users and what those users demand/want.
A "tactful" UI is optimized for other people's needs and wants.