Greetings. I mentioned else where, I was not planning on making a thread on this topic again.
However as I know it has helped users before in the past, and its not an easy topic to explain,
here is a random video on .fpm save files.

Suggested methods for setting up your GGC for map creation, avoid changes mid map.
- Preset your Terrain Type before loading GGC for optimal results.
- Build EBE structures on a Test map, Save structure and Bring Saved EBE Structures into your map build via placement.

Disclaimer:
This video had to be clipped as I'm not getting any faster, and would have went for too long.
Also sorry for no voice, text on screen. I decided the video should explain changes/edits made as shown.
Map bank/.fpm save file changes on time stamps here for each section shown, more edits can equal larger save files.
Also I do not cover Lightmapping data or how to set up custom terrain palettes, though I use preset/ Jungle as an example.
*Also please note. The choice is the user's, how they setup/build maps, class this as suggestive info only, use it if wish.
I also hope this helps users who have asked about this topic, possibly relating to large map sizes. All the best. Thanks.

0:00 Play test Blank saved map / Terrain type - Lush = (41kb)
0:05 Change Terrain Type - Jungle (in play test) = (944kb)
0:30 Terrain texture paint mode, imported custom .dds texture 512x512/256kb = (22,211kb)
1:00 Chane Terrain Type - to original used terrain type/Lush (in play test) = (21,184kb)
1:30 Change Sky Type (in play test) = (21,307kb)
2:00 Close GGC, navigate to Terrainbank/style file - to Jungle. New blank map = (41kb) (saves 900kb)
2: 40 New Map level = 41kb (terrain/lush) Load in two custom/paint terrain textures = (68,123kb)

3:40 New Map, place EBE grid (*note preloaded textures/not stock) make a EBE structure, press E = (14,337kb)
*The first placement of a EBE grid on map injects around 10,000kb + Texture file size.
4:17 Editing a saved map/EBE structure, importing New textures as shown = (28,751kb)
5:10 Adding/editing more textures to the EBE palette, plus new placement = (42,821kb)
6:15 Use the map as a test map to make an EBE structure (custom textures). Save EBE (found in = entitybank/user/ebestructures/)
6:46 Close GGC, update Terrainbank/Style - Jungle - New map, place EBE structure = (14,181kb) (saves 28,640kb)
*remember EBE initial grid placement first time costs around 10,000kb to use this feature. Keep this in mind.


Transcode video: 43.7mb 1080p