Cash games are the slow and steady grind. Tourneys are usually a slow and steady decline of your bankroll with occasional LARGE swings up. I find it very difficult to understand how some pros can play ONLY tourneys. It is very possible that they will be down for the YEAR by playing only tourneys. How can someone mentally handle that?
I used to use cash games to build my roll, and then play in tourneys with the profits. This kept me slightly up or slightly down until the inevitable large upswing - those sure are nice
Lately, I've been all over the place. After hardly playing any cash games for month, I was having a bad run with tourneys (this is how it is MOST of time time as a tourney player), so I decided to focus on the cash games again.... and now I've been having a bad run with those! Yikes.
I guess it's up to each individual to find the right balance for them. Just remember, your bankroll is going to have a LOT more variance in tourneys that it will if you stick to the cash games.