There's a good chance Cousins is nothing but a role player though.
Oh, for sure. I imagine he'll start as that and potentially expand that role as he gets more comfortable in Kerr's system, both on O and D. Whether he ever gets to his usual 25-35 mpg likely depends on (1) health; and (2) how comfortable Kerr is with him as a defender. Given Kerr's general preference for small, switchable Cs, the Warriors' impressive stash of same (Green, Looney, Bell), and the number of teams playing smallball these days, I imagine he'll settle in to more like 15-25 mpg, depending on matchup. Think souped-up Aron Baynes, with the pros and cons of 15 vs. 25 minutes roughly the same as the ones you guys have presented here re Baynes.
The first "role" I can see him filling right out of the gates is the second scorer in those Klay-as-primary-option units that have been stinking it up offensively for the last 2+ years while Steph and KD sit. Kerr has generally preferred not to stagger and Steph and KD's minutes too much (likely to optimize chemistry between them) which has typically resulted of 10-12 mpg of Klay on an island with deferential types like West, Iguodala, and Livingston, forcing him to think too much and make reads and plays, which has never really been his strength. Putting a beastly offensive initiator / focal point like Boogie on the floor with him puts him back in his comfort zone where he can run off screens all day, catch, and launch to his heart's content, with as little dribbling as possible.
Broadly, imagine Boogie combining what David West, Zaza, and JaVale brought last year, just at a higher level (especially in terms of scoring and rebounding). In terms of available minutes, give him most of the 18 mpg Damian Jones is currently getting, and you're basically there.
If I’m a Warriors opponent, I’m excited to have Cousins come back and start taking shots away from Curry, Thompson, and Durant. I’ll trade his 2’s for their 3’s all day.
He's averaged between 35.4 and 37.5% from three the last four seasons, on 5-6 attempts per game, or roughly the same number of as KD. He's also a fantastic and willing passer — 5.4 assists per game last season — so in addition to "taking shots away" from the Big 3, he should create some easier looks for them, out of the high and low post. And when he looks to score, it's not like he's a low-efficiency chucker like Carmelo: he scored his 25.2 ppg last season on .583 true shooting (116.6 pts per 100 possessions), which is basically Klay Thompson in terms of efficiency. (Not Steph or KD, but then pretty much no one is).
Generally (TLDR), I'm not too worried about the offensive impact. The defense is potentially more of a concern, as it is for any traditional center in today's NBA.
(Sorry, this should all go in the "Trouble in Paradise" thread — mods, feel free to move).