If you two have a strong and open communicative bond, this aspect could be an interesting and beneficial one for the friendship. If not, it could be a bit more difficult to deal with. You'll have a strong influence over your friend's thinking.
In conversation, you won't let them get away with a cursory treatment of any subject; when they skim the surface, you'll push them to dig more deeply and grasp the details of the issue. They may look up to you as a mentor, or they may feel constrained by your sobering influence. After all, who wants to be serious all the time? They also might get tired of having to supply ample proof every time they try to convince you of anything. But they'll become a more solid and thorough thinker through the course of their involvement with you.