Let's say an advanced weapon needs to be built lets say a Laser pistol. after research the manufacturing side has ALL the components but needs "Parts A" & "Parts B". In order to get these 2 parts is thru Alien UFO missions. After a successful mission you get ITEM 0 from the ufo. and the ITEM 0 needs to be broken down to RAW A, RAW B, RAW C ( for added difficulty it takes time to turn ITEM -> RAW ). Finally for "Parts A" to be made you need RAW A & RAW B and for "Parts B" you need RAW A & RAW C ( for added difficulty it takes time to turn RAW -> PARTS ). since you lack RAW A. you need to go on MORE missions to produce advanced weapons.
Advantage is that even IF you have ALL 100% bases in the whole world you still need to kill some ufo to be able to produce advance weapons. hence making HIGH end weapons scarce and Forces you to use the LOW tech weapons Longer or use (laser) weapons longer before you can use (Plasma) etc...
Prevents you from jumping Tech. So you have to use ALL the games weapons and figuring out for your self on how to use them properly and actually get bored using them and builds up the excitement and satisfaction of hearing the 1st laser fire or plasma hits, etc...
