Can you provide a sketch or picture of how the garage is positioned relative to the house?

Floor plan posted.

Hmm, getting things out and not moving the cars is an interesting point. The problem is Im on a sloping grade, and I’ll need steps on the door, which means anything coming out that door is going down a few steps. So the lawn mower or motorcycle is not going out that door.

i don't see a way around that with the layout. The only other place for a door is the other side. But that buys you nothing.

We are having a side door put onto our garage, but we are on level at that side of the house, so only a small step down. If you would have to have lots of steps, I say it isn't worth it.

Where will your garbage can be placed? If it's on the side of the garage, it will be useful to have the door so you can run out quickly without having to open the main garage door. In our old house we had another garage entrance, but in the home we live in now there isn't one. Personally, I prefer having one just for the convenience. As far as a security risk, I guess there is an extra one, but I don't think most people put an alarm system on that door though. I never had an issue before.

"Why would I want it . . . why would I not want it."

Because.

I always viewed ours as a way for someone to break into the garage, thus on our new build we did not add one. Doesn’t sound ideal in your situation.

Power outage and double garage door down and you can still get in and out of garage? I know you can release the overhead door manually, but our door is wood, so maybe heavier than newer ones. There are also lots of times in the summer when I am gardening or playing with the grandkids in the yard who now want "the other bike" and it's annoying to have to activate the ele. garage door repeatedly. But this might not be an issue for you.

Our first house and our present house has a side door and we love it. So convenient to get in and out of the garage without having to open up the big door. We use ours all the time. We keep all the gardening stuff in the garage and in the winter the snowblower, salt and shovels. No need to open the big garage door to let in the cold and snow and in the summer it helps keep out the flies and bugs. It is nice to run in and out of to grab a cold water out of the fridge we keep in the garage when working outside. We also keep our garbage cans in the garage and just take them out the side door on garbage day. We live in a low crime area, but it someone wants to get in they will always find a way, side door or not. We have a touch key pad on ours. Our property is on a slop too. Our side door is on the same side as yours pictured, but close to the garage door and is level with the ground. If it was in the back of the garage like yours we would need a step. Can you have it moved to the front of the garage? But you will have to see if you have enough room to swing the door open and not hit the car. It depends on how wide your garage is.

Another thing that is really nice to have in a garage is a stationary sink with hot and cold water for those messy projects.

I think if you store your garden stuff in the garage like your lawn mower this is a good idea.

Would it help for taking out garbage and recycling?

Perhaps, I have to take it to the front.

"Trash bins" must reside somewhere AND be easily accessible from the kitchen AND easily moved to the curb. Now is the time to consider options. Pay the FAR cheaper cost NOW for a door to the exterior (I'd put it at the hall between the kitchen & garage) and a service walk along the garage to the curb.

If you have dogs, I find side doors very helpful. I run my backyard fence to the point where it includes the side door, so I have an easy access to the front or the back without opening the garage door. Makes it so much easier to not have the dogs escape out the big garage door if you want to take the garbage/recycling out. Don't know what's above your garage, but the garage door opening does make noise that a side door opening wouldn't.