You should always tailor your strategy to your specific opponent(s) imo. I consider it a mistake to bet 50% pot OTR for value "because it's balanced" when you know this particular villain is a drooler who'll call any pot-sized bet. Equally, plain foolish to fire a bluff against a villain just because "you're at the bottom of your range" if you know damn well he's a calling station.

Balance is only something you really need to worry about against very good opponents. Against most, it's sufficient to simply avoid doing things which are absurdly transparent (only 3-betting AA**, always value-betting pot despite bluffing 1/2 pot etc.). It's a good intellectual exercise for coming up with a sound understanding of how to play the game, but not one I think we should apply super often. Even against unknowns, I would prefer to take specific lines designed to exploit player pool tendencies than I would a purely "balanced" approach.

I have been doing so for a long time (with good results). But is that enough to beat the higher limits, or must you practice another way of thinking in order to climb the limits? I mean multi-tabling you must practice a standard way of thinking right?

I think it's a healthy approach to think about balance to some degree but still utilize opponent-tailored lines. Whatever the jump is that you're taking higher, I think there will still be a lot of tendencies in your opponents (and the general flow of the table) that you can exploit better by not being in perfect balance. I think this approach also has the added benefit of it being harder for others to read into your playing style vs. that you would have a "standard way of thinking" against all opponents. 

I think you can reach a certain level exploiting fish with obvious leaks. However, when facing better players and playing in games with a lot of good regs I think a deep understanding of balanced ranges is very important. This will enable you to spot subtle leaks in your opponents game that you otherwise wouldn't.

Also it will give you a lot of skill in recognizing your edge (or lack of) against your opponents instead of letting variance and short term results be the judge of that.

A deep understanding of your own ranges will give you a lot of confidence that you are making the right plays in a lot of spots. For example when bluffing the river, if you know that you will have a value betting hand very often in a certain spots then bluffing without caring what the opponentdoes becomes a lot easier. It makes you more dettached from the immediate results. I mean if he calls it means that he would have paid off your valuebet had you been value betting.

Another example would be bet-folding in a certain spot. It is very nice to know that villain can't exploit you by raising since you know your own range and know that you have plenty bet/call hands in that range. Without this awareness you might be tempted to stack off too light in many spots. I think it helps keep your cool at the table too.

That said, whenever you see anything at the table that is exploitable you should exploit it. Some leaks are very obvious while others are more subtle and I think a good understanding of balance helps youdetect the more subtle leaks.

Exactly what Tom said.