Once a rescuer has determined your “general location”, they still need to locate you exactly, after all you may have moved in between the period you summoned help, and rescue actually arrives.
So having some means to assist a rescuer in precisely locating you, once they are in the vicinity is a good idea. A strobe or strong light would be good (in low light) or a whistle for day time. There are many other options too I’m sure I don’t need to list them all.
I have a free app on my Android (called “Morse SOS” – no affiliation) which will flash SOS with the screen and beep too. Now its not as good as a proper signalling strobe, and not as loud as a whistle, but I (almost) always have my phone with me and if I were “stuck” you can be sure that I’d deploy EVERY thing I had to assist in my rescue, including my smart phone apps !
I think that so often people assume that a smart phone is being used INSTEAD of more rugged safety equipment, personally I use my phone AS WELL as other safety equipment.
If you have a smart phone, why not put useful survival things on it - they cost nothing, take no space and you will never get a funny look if you take it as part of your EDC ?
Most folk who own a smart phone are well aware of its limitations (batteries, ruggedness etc), but it is handy to have none the less.
That’s my 2c