It is advised to leave it on.  This allows the bird to know if the signal is lost, what to do like allow you to cancel, etc. I leave it on so that once the bird it back within range and I get RC and FPV signals, I can canel the RTH and fly out again.

smart RTH just allows you to have control over your drone while its coming home.   with it turned off you cant control or move sticks to change angles and altitude.      either way,  smart or not your drone will still come home if signal is lost and your setting are set to return home.  

i may not be 100% correct with description of smart features as i have never directly executed a RTH or had it forced.      just relaying what i have read up on the smart rth,  i have not played with it first hand,   but i will be tonight for sure.   just stating this so I don't get crucified if i'm not totally correct with this this information.

Here are some links
http://wiki.dji.com/en/index.php/Phantom_3_Professional-Aircraft

http://forum.dji.com/thread-26899-1-1.html

microcyb Posted at 2016-4-6 17:03
Here are some links
http://wiki.dji.com/en/index.php/Phantom_3_Professional-Aircraft

Those instructions are out of date.  You need to download the latest instructions from DJI's download page, which incidentally was last updated on 30th March.

In the instructions, Smart RTH is as clear as mud.  The only way to know for sure is to turn it off & test it, or hope someone else already has & replies to this.  According to the instructions, smart RTH is just the button on the remote or in the app & shouldn't affect anything else, but really, until you try it, you won't know for sure.  I'm hoping to test critical battery RTH tomorrow if the weather's good so might try myself.

nigelw Posted at 2016-4-6 12:22
Those instructions are out of date.  You need to download the latest instructions from DJI's downl ...

Oh jeez!  LOL

pgrover516 Posted at 2016-4-6 17:40
Thanks for all replies, here is why I ask. I have always left "smart RTH" on and when I am out at a  ...

I had mine land a couple of days ago with a Critical Voltage Warning at 48% because I was using too much throttle on a cold battery (carrying extra weight).  Did you get any warnings?  It might be worth uploading the flight records to healthydrones.com to check the warning notifications in case you missed something.

quickpoint Posted at 2016-4-6 11:58
smart RTH just allows you to have control over your drone while its coming home.   with it turned of ...

I think this happened on a flight. My Battery gave a warning signal, I did not know which direction my Quad copter was flying, It was in visually range of about 150 meters.I was still in control of the Quad but it was still flying away from me, ( I am in  Pantic  Mode ) I then got the last Critical  battery warning.I landed the Quad out of my view over a small hill from the ball field.. I believe  I started the R T H feature after the landing, ( Question ) After landing and the  R T H it came back up in the Altitude Range and came back to me within 2 feet of my calibration starting point. Is this possible or did  The R T H signal activate before it landed. Thanks, It only had 2-3 small grass marks on the body and no damage.

pgrover516 Posted at 2016-4-6 14:07
wow that would give me a heart failure!

It was on my 2nd or 3rd time out flying . I had no problem on my 1st flight, I flew down to 2 green bars on the battery so I flew for about 15 minutes on the 1st flight. Since the  R T  H  problem I went out again and it flew ok, but I didn't go far away or reach any high altitudes

gosports1 Posted at 2016-4-6 13:59
I think this happened on a flight. My Battery gave a warning signal, I did not know which directio ...

posted this reply to this same post of yours in another thread  just copied and put here  

sounds like it wasn't completely landed and motors powered down,   it shouldn't take back off and return home after its landed no matter what the battery information is.   

also on your map you will see a little green line.  green line is directly from the drone to you/home. if you "get lost" flying only with the video feed which is very easy(even flying in  Line Of Sight) it can be hard to tell what direction the drone is facing.     if you point the drone to fly along the green line it will come back to you

also a feature that i believe is called "course lock" that you can engage that allows you to fly in some what of a "dummy" mode where the right stick forward and backward doesn't exactly move the drone forward and backward. but instead closer and further away from you.   this can be used and engaged to be able to just pull back on the stick and no matter what direction the drone is facing it will come back to you  

pgrover516 Posted at 2016-4-6 19:06
yes it did announce "critical battery landing now" and began decending even though there was still ...

Next time you're out, have the battery screen up & keep an eye on the voltages when it gets low.  Also, check the battery temperature as a cool battery will give you lower voltages.