That's inane advice. Knowing several opening lines is always an advantage.
It's how a beginner becomes an intermediate player.
It's how a beginner becomes an intermediate player.
There are some lines that are useful to know (Avoid various <10 move mates, mostly), but beyond that basic principles will get you to 1800-2000, IF you have the tactics and calculation skills.
Plenty of examples in the high ranks too - notably Magnus Carlsen (World #1) spends very little time on openings compared to most 2600+ GMs.
Knowing the SCO took me from 800 to 1600.
Thats absolutely ridiculous and SCO is a poor reference anyway. There are a lot of good opening books that cover specific openings to ever rely on an a comprehensive guide anyway.
I'll a little confused that you claim to 'know' it. You reviewed the entire book even if you don't play certain openings or defenses? There is a lot better use of your time.
To be precise - "knowing the mainline of common and popular standard openings from the SCO..."
No it isn't. Having a good grasp of chess tactics makes you an intermediate player. So what if you memorize opening lines? Your intermediate opponent isn't going to follow them at all.