It is down to cost, my mothers house already had the kitchen and wet room rewired, I had my mother in a EMI home, and it was uncertain if she would be let out again, if she stayed in then I needed a rewire to rent the house out, if she came out I needed a rewire to protect her when she did silly tricks like put an extension lead in a bowl of water as she thought the red neon was the socket going on fire. Estimates varied from £2500 to £5000 the problem was working out what was going to be done for the money, I would get comments like we will wire the garage for free, and no one would give me an itemised estimate so near impossible to compare prices.
Any rewire will involve some compromises, where the problem lies is in deciding the level of workmanship your willing to pay for. I made some errors, and the electrician made some errors, he also did some good things like using the old conduit so reducing the plastering left for me.
My son rewired his own house, in the main wiring between floors was done by removing the ceiling as he needed it re-doing anyway, he ended up putting in cables which were never used, specially the LAN cables, he thought he would need a LAN socket at every radiator to control the eTRV, but when it came to the crunch you can't get hard wired eTRV's you have to use wireless types. I did not fit enough sockets, and after the re-wire I must have fitted another 6 double sockets before my mother came home. I also did not run in enough TV cables, that was not included in the rewire.
So I have two RCD's and four RCBO's fitted, and the house is at least safe, even if some sockets are in wrong place, and not enough of them.
For my son he installed all cables while the ceilings were down, but many were not connected to anything, so for 6 months he had 4 sockets at the consumer unit, one went to caravan, one to up stairs, and one to down stairs, and one to washing machine all with extension leads. I got called to blown fuses more than once when son at work and daughter-in-law had done something daft. It was not what I would call safe, and I would hope no commercial electrician would agree to wiring up a house in that way. Today all finished and every mod con. Does things like auto put the central heating on when he is 10 miles from home. Server in the loft has all the kids films on, etc.
The problem he found was plan kept changing, which room was going to be kitchen, which room was going to be living room, so some cables still needed re-routing. What you need is a very detailed plan, exactly where each socket is going to be, I said I wanted 4 sockets in a bedroom, what I didn't expect that all 4 would be together with no sockets on the wall with cupboards on, reason was easy, cupboards stopped them lifting the floor boards, the other bedroom again all sockets in one area, this time because they needed to be 3 meters from the shower, can't really blame them.
They also sneaked in some surface trunking, I agreed surface trunking in corners of the room to reduce re-decoration, but stipulated non in centre of walls, moved a wardrobe after they had finished, and there was a run of trunking horizontal 3 foot high.
My problem was it all needed to be complete for mother coming home. Out of around 10 firms I tried only two could do it in the time scale. Now tables were turned when son was working as a sole trader, he had a few jobs on the go where he was doing a bit at a time, my rewire was done in 6 days with two men most of the time and 6 at the end to finish off, really electricians should not be working alone, they do need some one to help thread wires, so looking at say 7 days, so in real terms that means smallest split is 7 parts, really looking at no more than 4, so first fix one area could be done at same time as second fix in another, but to wire a room at a time is really a non starter. It could be split left hand side then right hand side, but likely you will lose power to some rooms for a few weeks. I had to move one of mums freezers to my house, and be able to turn other one off.
I said my son had a caravan, that was mainly because of heating, the family lived in the caravan in the garden for around 4 months, but no heating for a week in summer may be OK, in winter very different, he never intended to still be in caravan in the winter, but he was.
