it will only provide extra drag, which slows your acceleration, but helps you brake. That's why you choose a higher V1
sort of; you are actually choosing a higher V1 to minimise the distance required (i.e time) you have to spend accelerating thru the muck on one engine, to attain rotate speed following an engine failure; knowing that in the process if you STOP, your deceleration is assisted by the contamination. (this is now getting into balanced field length and all that stuff which is a whole topic in itself).
If you think about the extreme, if the contamination is so 'thick' that you cannot accelerate on 1 engine but maintain speed, your V1 would then have to be rotate speed to even have a GO option (simplistic - you actually still need to accelerate or maintain speed during the rotation)
However, now my next question, when is a runway contaminated and not slippery? Do slush and standing water only provide extra drag? I'd think it'd make the runway slippery to...
Today 18:16
If a runway is slippery, can it be 'draggy' at the same time??
In my post #6 above; I should have said it is 'safer to GO than it is to brake to a STOP
from a high speed (i.e higher V1's)