Editing Warhammer 40,000/8th Edition Tactics/Space Marines (section)

====Army Composition====
Deciding on what units to take generally comes down to what you want your force to accomplish on the tabletop. One school of thought is to avoid having too many various “types” of marines in one force, instead focusing on using lots of similar profiles in order to force opponents to attack units using suboptimal weapons. Using very little vehicles and lots of Infantry “wastes” your opponents anti-tank shots, for example. Or by having lots of heavy infantry and armour means that the small arms fire directed at you will be less effective. Other schools emphasize the modular nature of Space Marines and prioritize the taking of multiple styles of Marine units in order to more effectively deal with various threats. These two schools are extremes, and good list building most likely lands somewhere in the middle.
*The goal of making an army themed around a specific profile type is to reduce the effectiveness of your opponents shooting- an all-infantry army being more effective against anti-tank weapons is an obvious example, but similar principles apply to things like multi-wound attacks being overkill against single-wound units. However, this idea has one catastrophic flaw which should always be kept in mind: when the opponent is able to counter your chosen style and you don't have any units not of that style, they will counter you '''''hard'''''. Try to figure out what your enemy will be likely to use ahead of time so you don't pay for putting all your eggs in one basket!
**All scouts is one type. Or all Power Armour-traditional. Go all Primaris or all-regular Marine, do not mix. You want to either be all 2 wound models or all 1 wound models. The 1 wound models would all suck were it not for the awesome veterans: Sternguard kill things; Vanguard with 2 chainswords (4 attacks) that's a lot of attacks that does add up well; Company Champions can carry 1 stormbolter and 1 chainsword for 18 points and intercept wounds meant for the characters. Even Tacticals have the advantage of being a cheap source of heavy+special weapons, if nothing else. 
*The T5 family is all bikes, Inceptors and Aggressors. They'll be able to take a beating and things like Pedro Kantor+Aggressors are a powerful combo, but Bikes and Gravis-armoured Primaris Marines don't synergize very well with each other and you might end up leaving half your army behind if you don't pay extra for Repulsors (and it has to be Repulsors, Impulsors don't carry Gravis-armoured units).