A break is necessary even when you have a streak of wins because you need to relax, do other important things in life, chill and chill and chill and forget poker. This will stimulate your mind more and you end up with another winning streak.
If it gets boring due to the casino machine sounds and don't know whether its dark or day time outside, you need a break
Once, it got so bored, that thinking about playing in casino made be puke. I couldn't even think about poker for months. I was afraid thats the end of poker fun. Took nearly 6-7 months break before playing again and i played tournament and it was simply enjoyable. After that I only play once in a week/twice because i hate the constant sounds of casino as well as constant chip sounds and hate meeting terrible lowlifes. You would be surprised how many people you meet in a table, you would normally never meet in your life. Online is fun in that way that you just don't care whom you play with.