I think they are of use offshore, but its not easy and a balance of life risk situations.
In my post I said "1970s books where the dude is in the life-raft watching ships sail past."
For a start, nowadays, most are rescued in under 24 hours since the advent of EPIRB.
If one is still floating around a week later then the EPIRB hasnt worked/wasnt recovered, so no one knows youre out there.
After a week the weather has calmed or a calm day picked. Shipping is often very undermanned on the bridge and a good visual lookout is not kept well enough for any liferaft/dinghy to be spotted.
So the ability for one, on a calm day, to motor fast 2 or 3 nms to intercept a ship and fire flares near the bridge with the ability to return to the life-raft if unsuccessful, would be a life and death risk. But maybe better than a die anyway risk.
How the dinghy is stored for the passage is immaterial. Just make sure you launch it after the liferaft and before you cast off the foundering boat.
Dont just say: "We've got the raft we don't need the dink."
BTW I did a stupid thing a few years ago.... a friend said we are all going scuba diving to this great reef 1nm off shore. 5 couples in 5 dinghies headed for the marker buoy. I thought the leading dinghy had the exact location marked on his handheld GPS. Until I realised he didnt.
We couldn't find the buoy.
Thats about the time I realised I didnt bring an EPIRB or my mobile phone (didnt want to get it wet). My handheld VHF would have already been out of range from the shore. The shore was now about 2nms away and we were DOWNwind of in it the tradewinds of the Caribbean, next stop Mexico 1,000nms to leeward.
About then, the furtherest flung dinghy noticed the buoy about 500 yards/meters BEHIND us.
We had our scuba dive and then headed home... into the Tradewinds.
That was one long, worrysome ride home.
I count my blessings...