Farms are more like primary targets for bandits/monsters. Also main food supplier for towns/castles. Bandits extorting food/money or plundering and monsters eating people. Filler/target of opportunity/flavour etc.
If countryside is safe you will see prosperous farms if not you will see burned ruins infested by bandits/zombies.
Its way for bandits to get rich and famous(and more powerful) before facing bigger targets.
Also they add some flavour to the map and possible quests in towns/villages.
Like(branched quest tree):
*(1)Investigate – food stop coming from farm check it, come back with report, small reward
#Can be taken by bandits(A), monsters(B) or destroyed(C).
**(2A)Free farm – if farm taken by bandits free it from them and save farmers, take information from them, come back to city,medium reward
#Two options: It was roaming band of bandits:End quest
It was part of bigger encampment
***(3A)Find and destroy – find bandit camp and kill them, return for reward with bandit leader head
**(2B)Eradicate monsters – kill monsters, come back for reward
#Two options:It was part of bigger encampment (3BC)
It was roaming band of monsters:skip to (4BC)
***(3BC)Find and destroy – find monsters den and kill them, return for reward
****(4BC)Escort new settlers – escort caravan that will start farm again, small reward when caravan reach farm ruins
If farm destroyed skip to (3BC).
Or even small fetch/escort quest.
*Tax collecting – visit few (3 or 5 number can wary) farms and collect taxes from them, bring it back to town(castle)
*Gather grain(forage) – visit few (3 or 5 number can wary) farms and get grain(quest item) from them, you are followed by small caravan that carry this grain, bring it back to town(castle)
Its good idea if they are hidden at the start so exploring actually is rewarding(as finding stuff always bring some satisfaction).
Also thing about patrol militias and villages/towns/military outpost. I think they should be besieged for some time before battle start. So actually they can rescued.
Also it can be nice quest tree if company is send to relieve besieged town but can come to late.