Editing Warhammer 40,000/Tactics/Kill Team(8E) Guide and FAQ (section)

==What the fuck is a roster? Isn't that just a list?==
In KT you don’t prepare lists in advance, you prepare rosters. A roster is 20 models (for regular play, different limits in campaigns) which share a faction keyword but all of the other limits (points, number of specialists, individual model limits) do not apply. You tell your opponent what your faction keyword is (and he tells you), choose a mission and prepare the board. In competitive play, players show each other their rosters before choosing teams. This practice is also fairly common in casual games. 

Then you select the best individuals from your roster to accomplish that particular mission on that particular board against that particular opponent.

In practice you'll build a few set lists that you take out in predictable situations and try to merge them together into your roster. E.g. an Anti-MEQ list, and Anti-GEQ list, and a Anti-Melee list. Building the roster is a holistic process though. You have to balance all those needs together. Your Anti-MEQ list might be the greatest list ever built for that purpose, but if its 18 models and now you can't fit a response to Melee teams in your roster, thats not going to work.

'''Aren't rosters just for campaigns?'''

No, they're for all game modes.

'''Aren't rosters just for tournaments?'''

No, they're for all game modes.

'''Isn't this list tailoring?'''

Yes, that's the point. With so few models (a bunch of factions can't take more than 5 in regular size missions) a good all-purpose list simply isn't possible. Tailoring prevents faction and mission match-ups from screwing you and stops skew lists dominating. It's also a balancing factor for the factions with high model counts (factions that can only field 5-6 models at 100pts are at a disadvantage). Factions that field fewer models can pack their roster with loads of good options, factions that field lots of models have less room for alternate choices. It also counters horde lists because your opponent can see that your roster isn't able to do anything other than grot/gaunt swarm and can optimize for it.

'''Do I have to use a roster?'''

Yes and no. You'll always be using a roster but you can just put 100pts of models on it (assuming that your mission rotation only contains 100pt missions). Be aware that you're putting yourself at a huge disadvantage.

'''We just create a list every time without using a roster. 20 models is too restrictive.'''

Don't be this guy. The whole point of rosters is to force you to make choices. It's an important part of the game and an important balance factor.