In Skyrim, there are two types of cells: cells that reset, and cells that are "safe" (don't reset). Whether a cell resets is based on the EncounterZone set in the cell's properties. When a cell resets, most things will respawn themselves -- including containers. If a container does not have the
respawn flag set during the cell reset, its contents will be unchanged.
The designers generally made "dwellings" cells that don't reset (i.e. the cell's
EncounterZone has the "Never Resets" flag set to
true), but there are some exceptions. For "dwellings" that do reset, it seems that the devs tried to set the
respawn flags to all containers in the cell to
false, but there are definitely some oversights.
To find cells that never reset in the Creation Kit, browse the Encounter Zones in the Object Window (found in the WorldData section), and sort by Never Resets. For each encounter zone that you see where Never Resets has a value of Y, view the Use Info, and sort by Type. This will list all the cells that use this encounter zone.
To find places that reset, but have lots of non-respawning containers with the Creation Kit, one can look through the container items, sort by whether they respawn, then look at the Use Count for those containers. Oftentimes, you'll see that a container is used multiple times in one location. For instance, just now, I found that all the coffins the Riften Mausoleum don't respawn. Nifty!
Source: Long-time modder, worked on QA for Skyrim