A while after adding this mod to our game, autosaves started to take about a minute of time, with the progress bar at 0%. Removing the mod instantly restores normal save times (a second, game is in early stages with little area uncovered), re-adding it to the game immediately makes it ultra-slow, so it clearly is this mod.

factorio 0.18.26, lots of mods - Resource Labels Continued (after changing dependencies for 0.18) works flawless in comparison.

It's possible that save times immediatelly increased after adding this mod, but due to factorio saving in the background, we didn't notice.

More info: /resource-map-markers clear, without removing the mod, makes saves instant again, and /.. mark makes them instanlty slow again, so it has something to do with the map markers.

There definitely was a massive performance bug fixed in v0.3.6 of the mod. I'm not sure if this fixed was ever back-ported to Factorio 0.17. At this point, I'm mostly planning to stay with Factorio 0.18, but I'll see if just a version flip "works" without me having to fix anything...

Also, for reference (to anyone reading this in the future (like myself)), the dev/trunk version of the mod just has the two commands:
/chart-generated-chunks
/reset-map-tags-and-data
Both without any arguments.

That's indeed quite interesting - I newly installed this mod via the factorio mod interface in 0.18.26, and ended up with version 0.2.3. Factorio also doesn't list any updates when checking for updates, even though it does for many other mods - it lists 0.2.3 as most recent version, uploaded 3 weeks ago. I tried it on another copy that has never seen this mod, and the same behaviour happens, so as far as factorio is concerned, 0.2.3 is the current version for 0.18.

In any case, sorry for the kind of false alarm (even though something is wrong with this mod w.r.t. factorio), but never mind, I will likely stay with resource labels continued as long as I cna make it work, as it has less of an impact (this mod causes big pauses when generating terrain) and even displays human-readable resource names.

Oh, problem solved: when searching for this mod, I only got a result for "Resource Map Marker" - a different mod, so I obviously reported this against the wrong mod. Sorry for the noise here :(

To make good a bit, I downloaded 0.5.11 from here and tried it out. Unfortunately, the /chart-generated-chunks revealed the whole map (removed all fog of war), so it's not really suitable for adding to an existing game, but other than that, it seems to work just fine.

Well...

I just released 0.4.12 (for Factorio 0.17), and 0.5.13 (for Factorio 0.18). They are identical exception the required Factorio version.

/chart-generated-chunks is due to a feature request someone had to reveal all generated chunks. I would not expect either command to be used under normal "balanced" game-play. It is much more of a god-mod/cheat command for those that want it.