Alot of people hate chaperones, some deal with them.
Never bring a boyfriend as a chaperone
Only bring a non intrusive friend, who wont talk to you during the shoot and will sit quiety reading or something (you may need to pay them - i have done)
ALWAYS let the photographer know if you want to bring one, alot of photographers hate them because they get in the way and may cancel.
Chaperones should not be a replacment for checking references.
If your nervous on a shoot, explain to the photographer that you are inexperienced and ask for lots of help and direction.
I have only brought a chaperone twice, once I had only just passed my driving test and was terrified of the motorway so my mum came along, she sat in the spare room with the studio owner - and probably talked him to death. The second time, the photographer had no references so I paid my friend half my earnings to sit in the other room playing on her nintendo.
Since no one is actually answering... chaperones cause a lot of controversy on here. Some photographers don't mind them, but usually if theyre nearby rather than actually watching. You should check references thoroughly so that you feel you can trust the photographer, because lots have a no chaperone policy. If you feel the need to bring one you'll be limiting your choices of who to work with but if you don't feel comfortable enough going on your own then don't do it I suppose... uneasy models don't make for good photos.
If its out doors I like them cause they hold my lights and saves me setting up light stands hahaha
generally more togs hate them than like them , some don't mind them
general concensus is , you are a model its your job you should check references and handle it like any other job...
if in doubt don't shoot