Sure, but the issue is that you are more likely to encounter, by a great percentage, is to be legitimately delayed versus actually needing rescuing. To handle this inevitable situation, you have to debilitate the process of having a float plan in the first place. The person(s) you leave a float plan with are told to not react right away, or similar. Well, that's certainly a problem if you need immediate help, which also statistically is the more likely scenario if you indeed need help.
With a SPOT (or similar) you can easily check in periodically with the concerned persons to say "I'm Ok". They can then be asked to contact someone if you don't check in at designated times. Checking in with a SPOT is analogous to having a daily, or perhaps even more frequent, float plan, where you virtually close it by sending an "I'm Ok", and file a new one with them for the next short period of time. Furthermore instead of stating only hopeful intentions, the concerned persons know exactly what you did do and where you actually are, even when things are Ok.
As you can imagine, real-time position tracking is a major aid to search and rescue attempts. A float plan doesn't help much if you are off course, perhaps due to the very issue that is causing the need for help in the first place.
A float plan is essentially a one shot deal, and is only a hopeful best guess for the whole trip or for the larger segments where you intend to be in communication by other means such as reaching a port. Another problem is that even when things are Ok, the sailor is beholden a bit to the float plan just so their designated concerned persons don’t become alarmed and start sending help.
By the way, in addition to sending an "I’m Ok" message and tracking actual progress on a web site for your concerned persons, a SPOT also enables the sailor to send a different "Send Help", and still a different SOS message. The Send Help message can be configured to just go to those persons who perhaps have means to help you when all you need is some assistance and not a life threatening emergency scenario. An SOS message goes directly to the nearest help authority covering the area; worldwide.
If you actually need help immediately, there is no better system. Even a satellite phone requires you to determine your location, establish a satellite connection, then dial someone, who'll in turn need to determine who best to contact for search and rescue and contact them. With a Spot, you just press and hold a button for a few seconds and help is on its way, directly to where you actually are.
The only thing a SPOT can't do is self-activate. An EPIRP can, but only if the activation conditions are right. A float plan simply can't do any of these things, much less self activate.
A float plan is the simplest form of search and rescue planning. The only scenario that it helps with still requires time to pass and the resulting research effort to cover vast areas depending on the fate of the vessel. It is simply the least ideal system now that there are more functional alternatives.
I'm also a pilot in addition to a sailor. The original reference here was to aviation flight plans. Filing a VFR flight plan these days is simply rarely done, and usually only by student pilots. Filing an IFR flight plan is done for reasons having less to do with search and rescue and a lot to do with ATC and traffic management. And, even with flying on an IFR flight plan, which I do a lot, I more frequently change the plan (divert) in flight than I don't. The very times when I fly on an IFR plan are when I'm flying in and around weather, which is exactly when I most need to divert, or change from my intended plan. I could say the same for when I’m sailing. And, with an IFR plan, you are nearly always in contact with air traffic control. When you aren't, you are doing so in segments, just like sending "I'm Ok" on the SPOT. With ATC in America this is typically around 20 minutes or less.
Now, it is the case that the intended route on an IFR plan is used when a pilot loses communication with air traffic control, or doesn't show up at the intended time. However, air traffic control knows where they were last when communications failed, and many times the flight path, and its end, is usually tracked on radar. And the time passage is minutes to hours and not days or weeks. I.e., even here, it is other technology that is the significant advantage, well beyond the original hopeful flight plan, which accomplishes little, and only in rare circumstances.
