A) they don't have the 'time' to do that, &
B) they have a strict policy of varying matters, which if broken, they're sacked, so your 'stuff' is not worth losing a job over!
C) wouldn't you, & other family members' be there, watching, supervising, anyway?
It depends on your budget, how much time and how much stuff you have. My husband and I have moved ourselves (not really just us, we pulled in friends and family to help) about five times. Then once we hired professionals just to move the heavy stuff for us (whitegoods, furniture) and seeing how easily they shifted things that took us so much effort I would never go back. This time (I'm taking a break from packing to type this) we are getting professionals to move just about everything. I wouldn't get the full service where they pack it for you. We are packing everything in boxes ourselves then will get two guys and a truck to shift it. I used to worry so much about friends hurting themselves moving our stuff (someone did nearly get squashed shifting a huge heavy wardrobe up a hill once) and that's not worth it.
When we were newlyweds we moved several times and had friends and family to help. Last time we moved, I had two young babies and just couldn't face moving furniture and boxes around, so we hired a removalist. They were real professionals and made the day so easy for us. Now we have three kids and so much more to move with toys and clothes and extra furniture, I wouldn't want to get family and friends to do it, removalists might cost more but they sure do make the whole experience much easier.
I don't have a lot now, over the years I like to keep it down to what I like and really need!
So we would do it with family, cost nothing and I can take my time.
Last time I did use a removal company, they did some damage.....and never paid for it.
I emigrated from England to Australia so we had to use a removal company. They lost boxes and damaged stuff. I could not claim on the insurance because I could not prove they had lost the box. A real catch 22.
I have also moved by packing stuff myself and doing all the lifting and carrying. I think if I ever moved again i would pack myself and get someone else to do the lifting as I do not think i'm strong enough to lift stuff anymore.
I have done it both ways. The last time was with removalists, 400km to move everything, settlement on both houses on the same day. I did all the packing myself. There are so many considerations I don't think you can generalise about which is the best way to do it. I don't like moving house anyway, it's exhausting.