Image pipelines, not image tags. Uploads arrive from agents' phones at whatever size the camera produced, and the gallery still has to open instantly on a commute. That means derivative generation, sensible formats, real dimensions in the markup and a CDN policy decided early rather than bolted on when the hosting bill arrives.
Maps are the second weight. Clustering, boundary search, draw-your-own-area — all fine, all expensive if the query layer was designed for a list view and asked to do geography later.
Document packs are the third: leases, surveys, title reports. Storage, access rules and a viewer that does not force a download are the whole feature.