I do all the time. I don't care if the boss is grouped or solo. I love killing them as they seem to drop salvage more often and its fun nocking off bosses.
For yellow -> blue bosses I pop buildup and normally either kill them or drop them to the point where they just need a punch and they are gone.
Green bosses just take a normal AS and they are gone.
Oj->Red I will do 1 of 3 things. 1 If I feel that I have enough room to move around and get it done then I will kite them. If not and I have 2 to 3 enrages I will pop those with buildup and by that time I can take 3/4s of the Hp off the first AS, then just scrap them with a good 2-3 hits. 3rd if I really want to take the boss down but it doesn't look like a good place to kite and I dont have enough enrages ill look to see if I can go buy some (I will stop what I am doing to buy enrages and go kill a boss).
Where is the fun if I let them live?