Pigs can be a valuable addition to a diversified small farm by providing meat and manure; and helping to clear land.   They  are incredibly productive and are more efficient at converting food into meat than any other animal.  Pigs are very manageable for the small holder as they can be accommodated on a relatively small area of land.  While pigs are often viewed as dirty they are in fact no dirtier than any other animal and will not defecate where they eat sleep or drink. 
Pigs are intelligent creatures with a curious and sociable nature.  They enjoy the company of other pigs and get on well with other animals and humans.  However they are easily bored and this can lead to destructive behaviour.   They need root crops to dig up; they love food and eating; wallowing in mud and they need diversions and toys.  They like to "help" in the garden and be around humans, especially if there is a snack involved. They are quick to decide about the quality of pasture and will happily root up poor quality pasture or wet ground.  So be prepared to move them quickly if you don't want them to till the ground.  Conversely, they can be put to work with their digging or rooting behaviour taken advantage off. 
We do not keep pigs permanently but on a rotating basis with our other livestock.   On arrival the  young piglets will be confined to section of the garden as part of the rotation cycle providing manure and tilling the soil.  As they grow we keep the pigs confined in large comfortable yards with daily access to pasture grazing.   Pigs grow into large and powerful animals.  They respond to affection and are easier to handle if you treat them with kindness from an early age.  Quiet, purposeful, humane handling is essential.