There's certainly a lot of confusion as to what a script consultant actually does, but that's hardly surprising since almost all seem to do something different.
However in independent cinema there seems to be some consensus that outside help in script development falls into one of the following three categories: –
Script reader, Script consultant, Script doctor.
Broadly speaking a Script reader will assess the viability of a project for a producer and provide a 3 to 10 page written report called coverage (sometimes just called a script report), a Script consultant will be a long-time development executive with many tools and techniques at their fingertips who will work, often quite intensively, with a writer and suggest dramatic improvements, and a Script doctor will generally be a proven writer who will perform rewrite duties on an existing script.
Since you can't hire someone to alter a script you don't own, which one of the above you need depends on if you are:
The Writer –
If you're the writer and you still own the script, then a Script reader could tell you what isn't working (for them) but may have limited experience in knowing how to improve what you have. A Script consultant may be a better option as they can not only identify problem areas, they will be able to put you on the right track. They will also be very clear about how your project is likely to perform in the marketplace. If you've optioned the script to a producer and still want to make improvements to the script (good on you) then you should be able to get the producer to pay for a script consultant.
The Producer –
If you're just screening potential material you'll usually just use a Script reader to separate the wheat from the chaff. If you're seriously thinking about optioning or buying a script then you should hire a Script consultant for a professional appraisal. If you like a script, have concerns, but don't yet own the material then you should hire a Script consultant to work with the writer, if the writer is willing.
Warning #1: if your writer isn't willing to work with a Script consultant they may be a bit crazy.
Warning #2: spending money on developing a project you don't own won't make you own it any more. That doesn't mean you shouldn't do it, but it is a risk if you end up not pursuing the project.
If you own the material and have fulfilled your contractual (and union, and legal and moral) obligations then you can hire whoever you like, as long as you can afford them.
The Investor –
I'll include Sales agents in this category as well. Before deciding to invest in a project you will want to have a project independently assessed by a Script consultant, who should have one eye on the script and one eye on the market, and who can work with the creative team on reaching mutually agreed solutions to issues. A Script consultant will be able to ensure everyone is pulling in the same direction and that the writer, director and producers aren't all trying to make different films.
A note on Taste –
Tastes are different. I try not to impose mine on anyone I work with. That's not my job. My job is to provide analysis and relevant tools for the key creatives to optimise the script, while making sure everyone is apprised of the end goal and are not all pulling in different directions.
It's a delicate balance, and needs to be done in absolute agreement with the filmmaker, the sales agent, and any distributors attached. "The money" need to understand the creative imperatives, and "The talent" need to accept that this is a business not a charity.
The good news is that everyone wants to be proud of the end result, and it's actually usually possible to optimise creative pride with making a return on an investment.
– Robin TJ Kershaw