Been there! Done that! For 2½ years, in fact. (Feb 1999 to Summer 2001, so things might have changed a bit - but, from platers that I still meet, probably not very much!).
Different firms have different ways of working but, unless you're able to drive big commercial vehicles (such as artics) and/or live in area where there are lots of movements close together, it's unlikely that you'll make much money from it.
The firm I worked for (United Fleet Distribution, which has since been absorbed into the operations of British Car Auctions) ensured that it's staff were self-employed so that travelling time between jobs didn't count as working time. That meant that
(a) I wasn't paid for any such time ; and
(b) employment legislation (such as that relating to maximum working hours, paid holidays and minimum pay) didn't apply.
A typical day for me would be as follows:
Leave home (mid-Suffolk) at 0515 in the car that I'd kept overnight outside my house (having picked it up the day before), in order to arrive at the car auction site between Colchester and Clacton by 0600.
My first pick-up after that was often a new BT van that had been fitted out internally at Papworth Everard, which is 100 miles from where I was, so things would go roughly as follows:
0610: Having got the paperwork sorted out at the car auction site, start trying to hitch a lift.
0620: Get first lift to the edge of Colchester, arriving 0630.
0650: Get lift to edge of Ipswich, arriving 0710:
0735: Get lift to Bury St Edmunds, arriving 0810.
0830: Get lift to edge of Cambridge, arriving 0900.
Give up on getting lifts any further. Walk a mile to the Park & Ride site, get a bus to central Cambridge, arriving 0945.
Take bus to Papworth Everard, arriving 1030.
Get held up by bureaucratic idiots at Papworth Everard, leaving at 1130 to take BT van to north London. Get held up in Archway traffic system, getting to BT depot just as they're about to close for lunch at 1300 and beg them to process the paperwork straight away, so that I don't have to wait until they come back from lunch at 1400.
My next pick up is from a BT depot on the edge of Milton Keynes but I know that they close at 1630, so there's no way that I can hitch there. So I take the Underground to Euston, a train to Milton Keynes, a bus towards where the depot is walk the last half mile, arriving at 1620. I'm told that they don't accept collections after 1600 but, after a lot of pleading, they let me have the vehicle and I get away at 1645.
Get stuck in evening traffic and arrive home at 2015 with the van that's going to the auction site tomorrow (in readiness for 'more of the same')
So, at the end of the day, I've been on the road for 15 hours. I've not stopped for any food or drink. (I hardly ever got as much as a cup of tea while working). I don't count the first vehicle, that I delivered into auction as part of my earnings as I'd included that on my previous day's pay. I got paid £15 for the Papworth Everard to North London job and £25 for the Milton Keynes one but I spent £20 in fares. So I've made £20 for 15 hours work!
Yes, there were better days but there were also some even worse ones. (I was out of the house for 20 hours on one day, with no food or drink. After knocking off my fares, that I had to pay in order not to miss any pick-ups, I made the princely sum of £1).
I my last full tax year before quitting (April 2000 to April 2001) my total earnings were £8600. I worked 50 weeks of that year (simply because there was no work available over the Christmas & New Year period; I couldn't afford to take any holidays). Each week was never less than 60 hours and far more commonly 70 or 80 hours. However that £8600 figure wasn't my actual profit. I'd spent £1000 on fares, so I actually made £7600 for what (in terms of the hours worked) was around the equivalent of two full year's work!