Never seen it on an HGT.
The idea is that the water warms up the TB, helping vapourisation of the fuel. Can be helpful if petrol is lacking in anti-icing additives (unlikely now in the UK).
By passing it would possibly result in lumpier running from cold, or poorer economy on short trips.
I think folk do it just to make the plumbing neater -- all you need is some way of connecting the two ends up.