It will allow you to stay indoors and monitor the smoker, control the temp and the like. Some say it is a benefit, some not. Some say digital is a benefit while others prefer the old fashioned analog. Pretty much up to you and the wallet.
I wouldn't say the PID (wifi or not) is worth it 99% of the time. The sole occasion where I find it useful is so that I can crank it up higher when smoking a turkey. The analogs can't go as high as the digitals. Otherwise, the PID is a massive waste that just makes an otherwise elegantly simple smoker complex with more opportunities for failure.
Thank you very much for the replies. I appreciate all the input.
I finally got my si 3.5d and am doing my first smoke (ham). I see a benefit if the app allows you to change the pid settings faster. pushing all those buttons while leaning over the unit as it kicks smoke into your face is a bit of a turn-off. Still, $ 200 to have remote config and monitoring may be a stretch. Let's wait until my 15th smoke and I finally cry that configuring while smoke blows in my face is not an ideal situation.