Your experiences and your skills have made you UNIQUE and you have much to offer your colleagues. We learn from each other.

When you post a comment, your name, your photo, your headline are on display in the messaging string, staying top of mind with your network.
A comment will show your support to the colleague who posted the update in the first place and tightens the relationship between the author and you, building your relationships 1:1.
Algorithms within LinkedIn reward member activity and it’s anyone’s guess how it may boost your personal profile when writing a comment as opposed to a like.
If you’re a seeking a new position, your expertise is on display when you type a comment, demonstrating your value and depth of knowledge as a candidate to a recruiter who has stopped by to read your profile at a later time.
A “like” is shared to your entire network; however, your comment may start a conversation by sharing your expertise to your entire network.
Appreciation to D.B. Wenke