1. As a digital resume which recruiters/other people can find on their own, and can contact me if they really need to.
2. As somewhat of a soft sign that I "know"/"have been accepted as a connection by" people who work(ed) in the same company/area in the past. Kind of a signal that "maybe this guy is who he says he is".
Everything else on Linkedin is treated as trash. People I connect to are manually unfollowed almost immediately. Notification settings are modified so that I don't get any emails except inmails and connection requests. I thankfully haven't seen much spam from that till date.
Here are some firefox ublock origin filters I use to make the site a lot more bearable (basically removes the feed, the "news" sections, and other things which don't directly relate to the home page or connectivity). Only bad thing about this is that your list of connections won't show up; I haven't had the time to fix that yet.
www.linkedin.com##.feed-follows-module
www.linkedin.com##.ember-view.feed-shared-navigation-module.overflow-hidden.Elevation-2dp.left-rail-container
www.linkedin.com##.ember-view.pv3.feed-shared-news-module
www.linkedin.com###launchpad-wormhole
www.linkedin.com##.right-rail
www.linkedin.com##.ember-view.sticky
www.linkedin.com##.artdeco-card.share-box-feed-entry__wrapper
www.linkedin.com##div[class^="feed-shared-update"]