Hi, Danny. There are a lot of craftsmen that would tell you to patch the plaster is there are only cracks. If big chunks have come out, then drywall may be the best way. Check the guys at www.ornamentalplaster.com for their thoughts on repairs. As you will see, they are heavily involved in plaster repair and believe that is the only way to do it right. Part of the answer depends on your foundation and how much the house is moving and how much you have to spend.
Drywall is a reasonable alternative. One problem you might run into is stud locations. You will have to screw the drywall into the studs and finding them, particularly in much older homes, can be tough. The current 18" or 24" stud spacing did not always mean much way back when.... The screws have to be long enough to get a good bite. I would suggest that you use 5/8" drywall on ceilings for a little extra safety and ease of installation. I would think about 1/2" on the walls, too. Your window and door trim may make this decision for you. If you do not have enough sticking out into the room to allow you to install drywall without a major revamp of the trim, you could have bigger and more expensive problems if you have to build these out. Watch electrical box depth as you may have to make some changes or extra protection.
A float is like a trowel and I think the person that you are talking to is either saying to repair the plaster or repair it enough that big holes behind the drywall are not so flimsy that you can easily punch through them.
The drywall is a good fix if conditions are appropriate. It is quick, cheap and does not require a high experience level to do. As usual, sanding drywall mud--or plaster for that matter--will be messy.