Use it if instructed to because many people don't understand what airplane mode is.

Use it if you have 2G service still enabled on your phone as there is a very low chance of 2G interfering with certain plane components due to the higher power involved, though that is extremely unlikely, there's no benefit to leaving it on. Also, you really shouldn't have 2G enabled on any phone since it's commonly hijacked to send unsolicited text messages or enable man in the middle attacks, etc., and few providers use it anymore outside of some low density areas and other limited uses.

Use it if you have 5G, for now, since there is still research being done on whether the telecom industry is correct that the new C-band frequencies they're using won't interfere with altimeters that use close frequencies. This can especially be worrisome for low budget wireless chips that don't regulate their frequencies to spec on mass produced models. And poorly maintained altimeters that might not be well calibrated with age. The gap is small enough that it's possible that there might be some interference in real world situations.

So, for the average person, it's still worth telling them to just use it. There's no benefit to having cell service turned on during a flight. The real issue is that airplane mode should really only affect cell signals now and leave WiFi alone since planes have WiFi now and a lot of applications share between devices with WiFi, and leave Bluetooth and NFC alone since they're short range and low power and unlikely to cause issues. Just my opinion as an IT professional with electronics and wireless communication experience, but not an airplane specialist.