Intact male cats have stronger smelling urine, and if there are areas of your house where female cats linger they can start marking their territory by spraying it around. This is unpleasant for you and can be very difficult to stop them from doing, even post neutering.
If it’s a risk that he will get outside, and he’s intact, he absolutely will roam around looking for other cats. This will expose him to fight wounds and all the transmisible viruses that circulate around feral cat colonies.
If you’re confidant that you can keep him safely inside, you can always see if he starts showing roaming behavior, and neuter him then. If in doubt, it’s probably safer for him to neuter rather than keep him intact.