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What is the difference in sound, looks etc and does any specific company use either one of them? What are the Pro's and con's of them? Is there a difference in the different types when making basses and guitars?

Bolt on is your basic fender style. It's a pretty descriptive term; the neck is actually bolted onto the body. This can make for an easier time adjusting neck height (shims to raise the neck) especially with the micro adjusters that a few companies offer.

Neck thru guitars have a single piece of wood running the length of the guitar from the headstock to the bridge and usually all the way to the end, with quot;wingsquot; on either side to make the body. Neck thru usually makes for better sustain and easier access to the higher frets. They can be distinguished from set neck guitars like LPs and PRSs because they don't have a heel at the neck joint. Jackson/Charvel MIAs are a common neck thru. Many basses are made this way for the added strength.

i guess a pro of having a bolt on neck is that its easier to replace, not that many people snap the necks on their guitars, but say if you wanted to have a go at scallopping a fret board youd have the insurance of it.
im led to believe that neck thru creates a more resonant sound.