Enlighten me; windsucking and weaving?

[Kitei]

Now, I've come across them before, but it pops up on a lot of ads as "has been seen to weave, hence price", with a horse advertised for £1000 less than it should be, or "windsucks so is not allowed on my yard".

I'm not understanding why weaving would de-value a horse so much? Would just appreciate it being explained, aha.

 

[Bobbly]

Depending on how badly the horse weaves it can cause extreme wear and tear on the joints with the constant to-ing and fro-ing and also the shoes can be worn unevenly.

 

[Exploding Chestnuts]

Its a sign of a stressed out horse, and is very unpopular in yards as it is thought one horse will start off another, horse may be unthrifty.
It is a stable vice and must be declared.