In the long run assuming the age gap is only a year or two it's actually beneficial. First couple years are very hard but after that they are friends and entertain each other. Sure they fight but when they are getting along and helping each other out it's peace on earth.
Schedule can get challenging. Kids are all pretty much great by the time they hit 8 years old. It's a bear to get there though.
Plus they are paired up at boxing so they get most of their resentment out there :)
Multiple family medical issues mean if I were to have another kid, there'd be more than 5 years of age gap. Then it means different friend groups, different sports/activities teams, etc. Then add in that one parent works evening hours... Scheduling hell.