Unzipping Mods in your Mod Folder is a very bad practice to advise people to do. This could lead to a lot more problems for players and break a lot of mods and maps, because your changing filepaths by doing this. On maps especially this will likely break a lot of functionality and how items appear because of the way the author has set up the links to these items in the maps xml files or i3d files. You say "Why to unpack mods? - to fast edit xml-s mods, if you do not play in multiplayer." again you don't need to do this if your PC has 7Zip installed (Pretty much certain if running Windows10 as it comes with it) and have NotePad++ or have set 7Zip to point to your text editor of choice, you can load and edit the xml files directly within the zip. Anyway back to why unzipping a mod will likely break things for a player.
For example a map has its own custom silo for the players to store crops in. That silo is referenced in the i3d and the defaultitems.xml of the map with the filepath "$moddir$FS19_DondiegoMap/maps/placeables/farmSiloKomplex.xml" this tells the game to look for this item by going to the Mod Folder, opening the FS19_DondiegomMap.zip file and then browsing that for the maps folder, then placeables and finally finding the farmSiloKomplex.xml.
Now if you took this map and for example unzipped it to a folder in your ModFile for example we'll just call "Unzipped Map" for the same silo to appear in game when the player loads the map, you would have to change the filepath in a couple of files to now direct the game to look in the folder "$moddir$Unzipped_Map/FS_19DondiegoMap/maps/placeables/farmSiloKomplex.xml" for it to show up in game. No no offence to anyone but that is probably beyond the scope for a lot of people who play the game. And that's just the tip of the iceberg, imagine then changing the filepaths for textures, shaders etc for the models and objects within a map, in the i3d file. Yes you can edit the paths with a text editor if you know what you are doing, or you have the longer much for painful task of opening the i3d file with the Editor and going through every object to change path to point to where you've unzipped the mods textures to.
Now I don't disagree with the notion that mods downloaded from different sites, different authors may have issues where zip files have different levels of compression, have been packaged with different settings and therefore that could put additional strain on a system reading these files in game. However it's not going to make much difference to FPS or Performance because to be fair you are more limited by the game only using 3 cores and it also doesn't go above 30% cpu usage and 50% gpu, it's not a great engine for utilising and maximising the system a player has available to it. For many people the reading of zip files whilst playing will be performed comfortably by the other available cores and CPU percentage that is free whilst the game is running. However it can be a good idea to maybe unzip mods and then re-zip them yourself using what compression settings you are happy with and to ensure parity then that all the mods in your mod folder have same compression type so they will be read at the same speed.
FPS and Performance drops in game are probably more likely caused by bad quality mods and maps, where an author hasn't optimised them properly or incorrectly uses a lot of RAW files rather then the game's preferred format for example using PNG files instead of DDS, WAV files instead of OGG. Also many times I come across mods that have really bad texture setup, a author uses a 100kb diffuse file, then for whatever reason their normal file comes in at 900kb and their specular file also 900kb, this shows they are doing something very wrong when creating their textures or the software they are using to generate their normal and speculars is set wrong. As all the textures should be the same size. If an author takes that one object and uses it multiple times in the case of a map for example your going to be using an unnecessary 1600kb of data each time it appears.