The Army designed a universal carrier based on the BMP-3 and the T-90 tank, so any turret or weapon or sensors or whatever could use these vehicle chassis.
It means you can easily develop a BMP-3 or T-90 based vehicle... examples might be that you could make an IFV based on the T-90 (BTR-T... troop transport-tank based), or you could make a self propelled gun based on the T-90 (like MSTA, which is based on the T-80 tank chassis).
If you can work out all the vehicle designs based on those two vehicles then you just need two engine types for all the different weight vehicles... two types of tracks and wheels etc etc.
Their new family vehicles offer the same... one heavy tracked, one medium tracked, one medium wheeled, and one light wheeled platform to base all needed vehicle types on... so you get a heavy tracked tank, a medium tracked tank, a medium wheeled tank, and a light wheeled tank... (and another light tracked tank in the form of Sprut). All the tanks can share the main gun and sensors and systems and equipment.
For ships it means you can use the same hull and propulsion for a variety of uses... cruisers, aircraft carriers, landing ships, helicopter carriers, support ships, arsenal ships, intel/recon ships...
The Kirov class cruisers included 5 hulls, four of the orlan class were completed as Kirovs and one was completed as a huge intel/space support ship called Ural.