We tend to hold onto them until either we've got enough for a trip to the tip (advantage of a decent sized garage and large shed), or until we're passing near it as it's about a 200 yard diversion from one of the main routes out of town.
We've made about 3 trips this week, as we're clearing out the garage and needed to dispose of a pair of mobility type scooter that were beyond repair*, and a load of cardboard and wood offcuts.
*It was a shame to dispose of them that way as they would have made good chasis for go carts or similar.