To recover medical costs and loss of income while in rehabilitation
This is right. Income loss tops out at around $400/week if it's still the same as I remember it. So if you were making $1000 a week, but now only getting $400 a week, that might not be enough to cover expenses, especially if your injury takes a while to recover from. Some injuries take only a short time before being able to get back to work, but others may take a year or longer. Perhaps you borrow money, or dip into your savings to cover this period. The lawyer can help you file a tort claim or sue the other driver's insurance company to recover those losses.
And you never know how an injury sustained today may or will affect you down the road. There may also be injuries that are not apparent today that are caused by the incident. For some, it may mean a permanent loss or lessening of income depending on the types of injuries sustained and the type of work performed. The injuries may impact your ability to advance within your career. Usually your own insurance company will take care of you for around the first 12 months, but they might try to give you a cash settlement after that 12 month period instead of paying for ongoing care. The lawyer can help you sort out a reasonable settlement with your own insurance company and the other company.
In terms of documentation, a lawyer can also help you with what you need to do while you are recovering, so that you do not in any way jeopardize your accident benefits with your own insurance company, or filing a tort claim against the other party.
Remember, even if you are deemed not at fault, in Ontario, no-fault insurance kicks in and your insurance company takes care of you, to the prescribed guidelines that are set out by legislation. Those prescribed guidelines are like a minimum however and may not be enough.