What's the deal with Make-Up Air

3200 Sq ft home built in the early 90's that i've had since 2015. I had a new furnace and ac put in last year and also additional insulation added to my attic (along w/ air sealing). The insulation contractor did not do anything in my finished basement as I already had foam boards on my rim joists. As I was installing rigid foam boards on my rim joists i discovered an exhaust vent with flexible piping that just dropped right down into a vent in my drop ceiling. I wrote the model number down and discovered it was a Skuttle Model 216 Make-up air vent. At the time I had no idea what make-up air is but I read up on it a little bit and understand the basics of the concept. We have gas appliances including hot water heater, a high CFM kitchen exhaust fan, and gas dryer. Also reading up on the skuttle 216 manual, it seems like it's supposed to be connected to the return on my furnace. The way it's installed in my house is not this way. It literally is just a vent hole on the side of my house that comes through my rim joist and dumps into a ceiling register in my basement drop ceiling in the back corner. there is nothing else connected to it. My question is is there anything I can do to prevent all this cold air from coming into the home short of closing it? If i close the make-up air vent manually do i need to worry about backdraft issues? I feel like all of the effort going through insulating my house and then just discovering this hole thats basically allowing unfiltered cold air (or hot air in the summer) into my house is a huge waste of money. How would a make-up air system be properly installed and do all homes need them?

source https://hvac-talk.com/vbb/threads/2235794-What-s-the-deal-with-Make-Up-Air?goto=newpost