you can research economical and military bonus who will apply to all members of the clan

There are a number of benefits.  In an area around the SH (more developed SH, larger area) clan members enjoy bonuses to rss production, yielding and some minor military advantages.  Towns coming into that area can be evicted.  Once a building is developed in the SH special equipment can be crafted once it has been researched.  In Clan v Clan events points are scored by activities within the SH.

Most important is the equipment that needs to be researched in the stronghold ... and well you can get points for cvc from work you do in the stronghold.