As above it makes you look more professional ( as long as you have a reasonable one). I have had three jobs specifically from my site. Three £14 pm and one of them also had the works, fascias, soffits and con roof. Site only cost me £200. Plus lots of my customers have told me they checked out my site before ringing me in the first place as I have built my round by leaflets. (Still in process) I have had my site about 6 months.
Customers need to know you are not a fly by night. Giving them your URL, phone no. address, name etc is good.