I am using lifts for quite a while now, so I'll try to elaborate on your question here.
-> One: When you are using shoe lifts, obviously your balance will be altered. So if you try heavy exercising in the gym, doing squats f.e. it could be dangerous, especially if you are lifting weights. If you are using a running shoe (Asics), which gives you support on the sides it might work better, but an Air Max shoe has nothing like that.
I would definetly discourage you to use lifts, when you are running. You will mostly experience a turned ankle.
-> Two: Walking with lifts really depends on the shoe, and how much you want to "gain". Most of the lifts advertise, that you can use 5 cm lifts but in this case I made the experience that you have to think more conservative. The maximum I am using is 2-3 cm lifts, which equals about 2-3 "lift pads". You have a few issues here: A) Again balance. You more you put in, the more you will lose balance when you are walking (and I literally mean walking). It happened to me a couple of times that I turned my ankle. B) Your foot will look unnatural. Especially when you are sitting, and put one leg over another your foot will look elevated and everybody will notice that. C) When you have to take off your shoes everybody will notice that you are getting a lot shorter (again depending on how much you want to elevate).
Moreover, there is the aspect which I have mentioned in the beginning of this paragraph. Which shoe? The best shoes for lifts are classic winter boots, because you have support on the sides, and nobody will see that you have elevated with lifts and/or classic running shoes. In the summer you might have to tune it down a bit, because of the obvious reasons. :-)