Speaking for myself only I used to be an agency lady for years before becoming independent a little over two years ago.The advantages of working for an agency was that I did not have to worry about screening,photo shoots,and having to advertise myself for business.
After years I realized what the hell am I doing?The agencies I worked for had went out of business and bought by new owners which means new rules and BS.I did not like their new way of running things and I hightailed it out of there.That was enough for me I started reading different forums TER included before I went independent.Once I slowly got a grasp on being an independent provider I made the jump and have never felt so free!The disadvantages for me working with an agency was the cattiness of the phone girls who only wanted to use certain ladies or wanted to discriminate against certain races.Also,having to run around like a chicken with your head cut off was just not working out for me.
Now,I am only speaking of my personal experience with working for agencies.
There are some great agencies out here that are very fair and treat their providers right and some not so good.
But,I would think for a guy it might be a lot easier to set up a last minute or same day appointment with the agency versus an independent especially if you have already been a client of theirs.Also,the advantages would be for the provider who is starting out and has no clue about screening etc she might want to start with an agency.Some providers don't mind screening and advertising themselves and some do not want the hassle of it so working for an agency is more convenient for them.
Just my .02