There's two main types of 35mm negative film: C41 process and silver B&W.
C41 processed film includes most colour film and also some types of black and white film (film such as Ilford XP is a black and white film which is C41 processed). Advantage of C41 film is that most of it can be machine processed so turnaround time is quicker and cost is cheaper. Since the film is machine processed, it doesn't really matter where you send the film too as the results will be more or less the same.
Silver B&W film includes almost all black and white film like Kodak Tri-X and Ilford HP5, and is hand processed. Film is loaded into a plastic container by hand, chemicals poured in etc all by hand, hang drying the negatives. Hence turn around time can be 2-4 days for this. Type of developer used, concentration and timing also affects the results. This is actually quite easy to do but time consuming, and is the type of developing most people here do at home.
Regardless of film type, a good photo lab will handle your negatives carefully to prevent scratches, and have the equipment to scan the film in with more detail.
