depends on the job if you can get there and start early 8am you could do the job and still get back to do a few of you local work making a good £££ day
as the travel there could be done on own time not work time if you get what I mean
What's the difference between your 'own time' and 'work time' when you work for yourself?
lol i don't get that 
well if its a 2 hours drive and you can get in and start at 8am you set off at 6am (own time) get there for 8am do job , then back to your work say 11am using own time (sleep time)
or if you use work time at set off at 9am start at 11am back to round work at 3pm days over why bother doing anything else
it all depends on what your works like and how busy you are , how much you have in the bank , if your over worked then most wont travel , if they do for big jobs they want a heap load of ,money to upset there rounds why travel if there earning good money on the door step
how ever if you want to build , make more money , or not upset your round to much buy using own time (sleep time) it doesn't up set your nomal work to much , allowing you to travel and maybe quote alittle cheaper as your not dropping 4 weekers to do say a 12weeker