Elite enemies spawn at the end of Escalation Sites and can drop faction ammunition and modules (Sansha and Blood Raiders).
Expedition sites escalate to another location that is either DED-rated (DED 3/10, 4/10, or 5/10) or unrated (1-4 locations).
https://wiki.eveuniversity.org/Combat_sites
Sansha Hideaways and Refugees escalate to a 3/10 rated Sansha's Command Relay Outpost, which can be completed easily in a T2 tank-fitted cruiser.
Blood Refugees (exclusively) escalate to a 4/10 Mul-Zatah Monastery. This can be run in a T1 passive Drake or drone cruisers (Vexor/VNI/Stratios) with 55+ km range. In the second room, destroy the structure, bookmark it, warp off, and return after 3-5 minutes.
2/10 sites are only found in 1.0 and 0.9 systems as scannable anomalies.
3/10-4/10 sites appear in systems rated 0.8-0.3.
Sansha/Blood Vigils are scannable unrated sites that can drop mid-grade implant BPCs or implants (Shield Buffer for Sansha, Armor Buffer or Neutralization/Cap Emitter set for Blood).
These sites can escalate into expeditions with up to 4 locations. Best ships to use are well-fitted T2 Cruisers, Stratios, Gila, or Navy Battlecruisers.
Loot from DED sites is completely random, with potential drops worth 1-250 million ISK from 3/10 and 4/10 sites. Vigil implants can be worth up to 400 million ISK.