Crate training and having dog crates are practical safety measures for a multitude of reasons.
Aside from the typical house-training of a puppy....
Dog crates keep your dog safe from others
Dog crates keep others safe from your dog
In regards to keeping others safe from your dog, your dog may very well not be aggressive in any way, but aggression is not the only thing to protect from.
a.) toddler or young children visitors who may be accidentally tail-whipped or knocked down by a dog.
b.) visitor who may be severely allergic to canine saliva and cannot risk being licked or sniffed (and potentially touched by drool.) (I specify saliva and not hair/dander because that is going to be present everywhere in the house of a dog-owner..so ppl w/ severe hair/dander allergies should not enter the house. I personally know one lady who is fine with hair/dander but does have extreme allergic reactions to dog saliva.)
c.) visitors who are terrified, just plain terrified of dogs. Some of my friends are, I still like them to come visit me, but I must put my dogs up when they do.
Keeping your dog safe from others
a.) babies, toddlers, children... if someone else's children are visiting my home and are not under eagle-eye supervision, I want my dogs crated and not accessible by children....too many horror stories of what kids have done to pets.
b.) utility/repair person in the house, I don't know them, they don't know me or my dogs, I feel best having most of my dogs put up, maybe keep just one big one out with me...just in case utility person is a predator 0.o besides, you never know when these people are going to leave the door/gate open.
c.) should the authorities ever visit my house for any reason, I want to be able to put my dogs into a place where they can be safe. I once managed a show breeding kennel for an AKC Judge, she told me once that she had been downstairs in her nightclothes tending to a female in whelp when an officer came down her stairs, in her house, with his gun drawn, apparently a 911 call had been made, saying there was an intruder in a house, however the officer was at the wrong residence. However the officers insisted on doing a sweep of the house to make sure anyways. They allowed her to put her dogs in their crates before doing their search.
Also, if something happens to you and you end up in the hospital, unable to communicate, authorities will visit your home to notify any other potential residents and if you have pets in your home and no one is available to take care of them (or no obvious information left for officers to contact someone to take care of pets,) then dog warden or animal welfare people will be called to take the animals out of the house and care for them. It is in your pets' best interests to be familiar with crates.
Also, if you have more than 2 dogs...or even 2, you may need to have 1 or more dogs crated when not supervised so that there is not a dogfight when you are gone.
I really enjoy having my dogs as housepets, I like leaving one or two free to roam the house when I'm not present, however for my dogs' well being, all of them are crate trained and kennel trained as well as house trained. I cannot predict my entire life, should something happen that my dogs must be put in crates or a kennel, then it would make it that much easier for them if they were already familiar and comfortable with being crated or kenneled.
As for travelling...wire crates can be folded down and take up less room. plastic crates may offer a little more safety if there was a car wreck or falling debris. I am not very good myself at always crating my dogs for car travel, but should I be involved in an auto accident, or even pulled over by antsy police... my dogs would be so much safer in a crate in the vehicle, if not that then at least in a harness and buckled in.
Fabric crates IMO...(unless we are talking a tiny dog carrier carried like a purse)...are nearly useless, in disaster situations dogs may need to be transported by carrying it in it's crate, which cannot happen with fabric crates. Plastic airliner crates are best in this situation.