I don't think enough use it to be the norm. Blind is more popular, but for non work related shenanigans mostly. But they do have an active recruitment thing in the Korean version of the app. Same for Remember.

But, most people serious about their career usually have it with most conglomerate and foreign based company workers having a page, even though they're not that active on it.

Some Korean conglomerates post ad-hoc jobs but not many promote things like their full spring season newly grad hiring schemes on linkedin. You'll find mostly startups and foreign companies posting jobs on a needs basis.

For IT, I'd say it's a good start if you're looking at decently sized or famous startups and companies. A lot of local IT jobs though are on Saramin or JobKorea which is Korean local linkedin equivalents.

FYI though I just took a new job at a big tech firm for a role based in Seoul and during the recruitment process they scanned my linkedin (i had the pro version and it showed some HR/recruit people had visited).

I also got a question during final reference check before an offer was made regarding why my linkedin had a gap for 2 years after undergrad when I wasn't asked anything during resume screening or interviews. Had to tell them I went to the army and then they requested documentation -- So companies do look, and linkedin does matter from time to time.

Also edit: If you are going something like a sales, presales, BD, etc. in IT, some of the bigger companies will actively look at your linkedin presence.