yeah the ecu does do something with the speed sensor. I think it has something to do with choosing to run on closed loop with the oxy sensor. Plenty of people do run without them with no problems though.

and do u think it will effect the ecu if i take a brach to the speedometer.

Apparently sometimes they can have idle issues when speed sensor is not hooked up but there are ways around it. If it's not too hard i reckon i'll hook mine up, i want it to run as smooth as possible.
If my mum needs to use the car, i don't want it stalling on her...

signal comes from sender to speedo is processed then sent to ecu. plms does a box to replace speeo