Hi there,
Lawyers are allowed to provide a larger range of services from paralegals and consultants, such as litigation. However Paralegals specializing in immigration, and registered immigration consultants (RICs) specialize in immigration and there is a greater chance they will know about the ins and outs of the system as many lawyers only deal with immigration cases some times (and only serious ones) or someone on their staff who is not actually admitted to the bar might handle it. Also RICs and paralegals are cheaper.
We are, of course, biased in this regard.