Using an attorney can save you time you would otherwise be using to study up on the immigration process and might save you worry that you are not filling something out wrong. However, it costs money and you need to research attorneys to find out who is good and who is for real and who is a scam artist.
Doing it yourself, even if it's a bit more work puts the control in your hands, not somebody elses.
The process with immigration will not be faster if you use an attorney.