It's designed to help weak/mobile/indoor nodes in poor radio locations, not routers. When you favorite routers or other strong nodes, your CLIENT_BASE aggressively rebroadcasts their traffic (acting as ROUTER), which can actually suppress better routing paths and add unnecessary congestion. The feature works best when you favorite only your personal handheld/EDC devices that need the boost from your strong base station. Favoriting already-strong infrastructure nodes defeats the purpose and can negatively impact overall mesh connectivity.

This is entirely dependent on your mesh topology of course. In our larger mesh with a lot of routers in advantageous locations, a client base favoriting a router would do more harm than good

Another more informed guy in our group just posted this, seems like I may have been wrong https://meshtastic.org/blog/zero-cost-hops-favorite-routers/