If there is one thing that makes a difference equipment-wise it's a good bar versus performance in the competition lifts.
It's not just a matter of knurling (that is actually the least important element).
A good Olympic lifting bar has...
A lot more spin (bearing vs. bushing) which makes a HUGE difference in racking your cleans (much easier to do the turnaround to rack the bar on your shoulders) and also in getting under a snatch. On the other hand, a lot of spin can hurt on the bench.
A 28mm thickness while regular gym bars are normally 29 or 30mm. This makes a big difference especially in the snatch if you have small hands.
A lot more whip than a regular bar. A skilled lifter who produces a lot of acceleration can use that whip to create more upward momentum and lift more weight. At first it can hurt your performance on the squat because it "bounces" more (flexes more) and if you don't time your movement with the upward swing of the bar it can be harder to lift.
It's built tougher and can withstand the abuse of being dropped a lot better.
That having been said you don't necessarily need an Eleiko (top of the line). Thanks to the popularity of Crossfit there are now more and more decent bars that come at a decent price. Just make sure it's an Olympic/weightlifting bar (normally the 28mm and bearing and a high pounds per square inch is what you are looking for).
I have 6 bars in my garage:
Pendlay bearing bar (they also have a bushing one)
Rogue weightlifting bearing bar
Vaughn bar (bushing)
A generic bar (that I use for squats and bench)
Tonic performance bar (bearing)
Old York competition bar (back when York had good bars)
And also lift regularily with a Pendlay bushing bar and Again Faster weightlifting bar.
And it makes a difference which bar I use. The Pendlay bearing bar is a decent option for those not wanting to pay too much. Again Faster has the Klokov bar out that looks promising since they used it for the Klokov power weekend so you know it "works".