The major consequence of the professionalization of a legislature is, for better or for worse, more legislation.
Political scientists say that a legislature is more professionalized as its members get higher salaries and more staff and as they meet for longer periods each year. All of these things make it much more likely that more legislation will be proposed and considered. If legislators get paid more and have more staff, they will be able to draft more legislation because they will have staff to help them and they may not have to have another job that will allow them to make a living.
This can be seen as a good or a bad thing, depending on your political ideology. Conservatives will generally see this as a bad thing because it invites more government intervention in areas where government should not interfere. Liberals will be more willing to accept a greater amount of legislation because they are typically more receptive to government intervention.