What is a speed sensor good for?

The speed sensor can help with speed accuracy in conditions where GPS reception is problematic.

flocsy🤠 said:

so what would a speed sensor add?

Very useful for measuring accurate distances during MTB rides where there are many sharp turns or switchbacks.  

Also if you are interested in speeds in high speed sprints, can be helpful.  When changing speed rapidly GPS data is pretty averaged/smoothed, so if you go from 14mph to 30 in a short sprint... the speed reading is always behind a couple seconds / mph... really never catching up until fading.   How useful that info is... meh... but for say a short strava segment if you were looking back at it wondering why you were going slow at the start even though you accelerated early... likely due to a bit of lag in gps.  Similar idea of why on corners will often show it slightly 'cutting the corner' 

Speed sensor will also go to autopause much sooner, not waiting as long for it to wind down your speed (or start back up from stop)

Also helpful for getting some sort of 'speed/distance' while on a wheel on trainer or rollers.  Not that it is accurate/real... but I have found it just fine in the past (hard interval would be around 25mph... easy spin 17-18mph) (especially pre power meter for me, gave me a decent target on intervals).

speed sensor also has shortcomings... in sand/snow/ice, will give distance for slippage and/or lack-of-distance on locked up rear wheel braking.  both minor issue much of the time.

A speed sensor allows speed measurements in basically ALL conditions - even in tunnels ;-)

I personally don't trust speed values from GPS (this distrust dates back 15 years), so I simply put a speed sensor on all my bikes.

If you never had the impression that the speed values of your EE2 are off sometimes or you don't consider this as important for you, you simply don't need a speed sensor.