I've never used them. The only times I could see a blinky mode being useful in my modern day-to-day life is:
1) If my car dies and I want to warn oncoming cars... in which case a beacon or SOS mode would be useful, but a strobe is a bad idea (as pointed out above). As this scenario is not outside of the realm of possibility, I keep a Xeno E03 with diffuser cone in my car for this purpose.
2) When recreating in the wilderness (camping, kayaking, hiking, etc.), it might come in handy to have an SOS/beacon mode to signal to rescuers if I get into trouble.
3) I work in the city, and am sometimes entering a parking garage at late hours when I head home. On those occasions, I keep a 2*AA light set to strobe mode handy in the outside (unzippered) pocket of my laptop bag. I don't know that I'd have the b*lls to try to use it if accosted, etc., but at least it's an option as a last resort when there's no other alternative :\
Since I'm risk-averse in general, I have thus far successfully avoided the need to actually use a blinky mode in real life; by properly maintaining my car, being cautious and prepared when in the wilderness, and being alert in crime-ridden areas, I hope to keep it that way. I don't mind having SOS/Beacon hidden but available as insurance for scenario #1 and #2. However, without training on how to properly handle scenario #3, I'd think it might do more harm than good to whip out a gun-looking item like a 2*AA flashlight with the intent to strobe someone who's threatening me... it'd probably be safer to just hand over my wallet, or run.