Is it worth to memorize idioms?

Dear 50groszy,
I'm happy to respond. I see that AjiteshArun already gave a good response, but I want to give a more lengthy response.

I have a few things to say to you, my friend.

First of all, think about why the GMAT has SC at all. We live in a modern world in which many folks get to know each other through writing. Right now, you and I are getting to know each other through writing. Once you have your MBA and are in the business world, you will make new contacts all the time through your writing: new customers, new suppliers, new partners, new advertisers, new lawyers, new competitors, etc. etc. In the business world, people are always looking for indications of "should I trust this person I don't know?" Furthermore, psychologists have documented in great deal the powerful impact of first impressions. If our first impression of someone is relatively low, then it would be 10x to 20x harder for that person to make any kind of positive impression on us. If our first impression is low, then we are inclined to be critical. If our first impression is high, we are inclined to be accepting and forgiving. That's just how the brain is wired. Now, if you were making your first impression to someone in the business world, think about how your opening email or web comment would sound if it contains idiom mistakes. ("My company is able for helping you to . . . ", "Our software will prevent your system to crash at any time." ) In that second example, the idiom mistake almost sounds as if the person is saying the opposite of what he actually was trying to say! Not knowing idioms can distort or change the meaning of what you are trying to communicate, and this can cost you sales and valuable business contacts. The GMAT tests idioms precisely because not knowing them can cost you money when you are in the business world!!

Another thing I will say is as follows. I don't know you, so I don't know your GMAT ambitions. Perhaps you would be perfectly happy with a mediocre GMAT score. But if you aspire to a 700+ score, if you aspire to GMAT excellence, then it would well behoove you to embrace the habits of excellence. Part of the habits of excellence is not taking anything for granted, not assuming that anything is of little importance. Any energy you spend criticizing the GMAT's priorities is energy you are not spending on achieving excellence. Excellence is all about jumping in and doing the hard word even if the "point" is not immediately clear to you: work first and ask questions later! Excellence is all about not allowing yourself any concocted intellectual excuse to prevent you from doing the hard work of achieving mastery. Idioms appear on approximately 1/3 of all GMAT SC question: that's way too big a region to write off! If you start playing the game of "If I do X, then I can't do Y," that's a scarcity game. That's a guaranteed route to a mediocre score. The attitude of excellence involves finding the time and the energy and the motivation to do both X and Y. The mindset of excellence is a "both ... and" worldview, not an "either ... or" worldview. Few people can muster all the stamina and courage to live out the habits of excellence consistently. That's one reason that so many people fall short of 700 even when they have the best prep material at their disposal.

My friend, I am extremely ambitious for you. I want to support your success in any way I can.

I hope you find these reflections helpful! Please let me know if you have any questions.
Mike