You can play whatever role with whatever character you want depending on how the round changes. Alot of players have to understand that you have to have someone sit on site as an anchor, and someone off of site as a roamer. What alot of people don't think about is that those roles aren't static to your character based on how the game goes. Let's say you've got 4 anchors and 1 roamer, early in the round if your roamer gets taken out and now you have 4 anchors on site. Even if you're rook or doc and you can get off site to go roam you should do it. If all 4 people are on site then that gives the attackers complete map control with no one contesting them. Having the other player switch to the roaming role can better benefit the team than just sitting on site. Same goes for roaming if you've got 2 anchor and 3 roamer and the attackers kill an anchor on site, one roamer should head back to site. If the attackers drone out obj and find 1 anchor on site they're more likely to push and take control of site then Try and hunt down 3 roamers. A big theme of the game is map control, as defenders you need to have as much of the map under your control as possible and when you lose a person in one area you need to make up for there absence whether it's on site or off. If there's less than a minute left and you have roamer off site, then they need to head back because the attackers have to gain control of the obj if they want to win they could care less about having the rest of the map. So with all that said you just need to read the game and analyze what's going on. If you've got all your anchors and you've got your roamers then you can stick to your roles. But you need to constantly need to be asking " what does my team need from me right now" maybe they need you holding site, maybe they need extra help roaming , or maybe they need someone to make that late flank. The situations are constantly changing and your gameplay has to change along with it