there are many advantages of tour guide, tour guide can enhance the surprise factor in your travelling experience  as that person have local knowledge and know how to deal with problems. the factors like safety, planning your trip which reduces the wastage of time or leads to no wastage of your time. 

the cons of the tour guide are practical as firstly, it lacks flexibility as to the time limits they provide for. But you can avoid this also by arranging your tour guide till the time you really want.  Secondly, is is not cost effective. you will have to spend some money from your pocket for the above mentioned advantages!

Finally, it's your call what to like most