If there's one resource people who play a lot of Path of Exile tend to ignore, it's time. There are currency Path of Exile items and whatever else you can put up for trade, then there's the 24 hours in a day that you get to make use of to do stuff, including playing the game. Many of those who are indeed serious about the game don't think about it as much as most others as they've dedicated their time and energy into playing the game, but they still need to sleep and get daily life things done.
Therefore, being able to experience as much of the game in as short of a time frame as possible is crucial. That includes being able to farm and grind very quickly, and that's quite a big part of the game. Being able to clear areas in the game that yield the most amount of experience and items without being too difficult is a big part of the game, and the builds and skills that go into doing what you intend to do is a major part of that process.
But do take note that before you can put attention to clearing speed, you must first understand that the main aspect of gameplay is always survival. You have to take care of your character's survivability first, especially if you're playing in a hardcore league. Dying is a waste of time even in standard league, so you'd want to pile on the health, energy shield, and/or defense first before venturing forth. If you are going with a build that guarantees survivability, make sure that you follow what's necessary in order to not have your character be squishy.
Being able to clear areas fast means being able to kill as many enemies as possible with as little effort as possible while staying alive. That means you'd want skills that hit multiple enemies at once, whether it's splash, area-of-effect, or just something with a sweeping arc or linear penetration. There are quite a few skills that do just that, like Earthquake, Ice Nova, and CoC Discharge. These particular skills don't require aiming; just casting them can kill everything in front of you as long as you can deliver enough damage.
There's also Shield Charge, which is quite powerful. There's also Flicker Strike, which is also powerful when combined with the right support gems. Everything else you have to aim and click with in order to use. As long as you get the necessary practice in order to make use of them, then you should be able to use them in a pinch when you're surrounded by dangerous enemies in a very hostile area. That's a big part of what playing Path of Exile is all about.
The thing about Path of Exile is that with the minuscule drop rates of PoE items, clearing speed is almost a necessity if you really want to get ahead. Therefore, once you've mastered the fundamentals of the game, it's time to get good with combat and turning your character into a death machine.