Online check in allows you to secure the seat of your preference.
Prior to online check in most airlines now charge you to select the seat of your preference which is a rip off.
Yes, i have been twice over my 24 years in Thailand.
Once which was Oct 2020 during Covid, absolutely fantastic, no one about, clean beaches, clean water and very cheap.
Once post Covid - horrible, full of tourists.
I will not return.