Less about whether the cost is really worth a full preseason v an abbreviated one, and more to do with the reputation of the club.
Look at clubs like United, chavs, City. They have a reputation of spending the money, and as such as soon as they come in for a player the selling club slaps a nice rich tax on the price. Players keep getting more eexpensive for them each window, it's a spiral.
Look at the dippers, they've become an easy mark because they don't negotiate. Now they're bettering the over-bid price for Bats to get Mane.
So what's a £1m here or there? A lot, because once you get a reputation for caving, rather than being tough negotiators, every club we talk to is going to inflate their price and hold our feet to the fire knowing we'll cave. Add it up over a window, and it's worth an extra player or being able to give raises to our deserving players so they don't get their heads turned.