There is no simple answer to this question. Every case is different. Every plaintiff and injury arising a motor vehicle accident is going to be unique. No two cases are exactly alike.
Ideally, you should not settle your case until you have a long term picture of your injuries. Once you settle a case, you generally cannot go back and ask for more money. You do not want to be left in a situation where a seemingly small injury progresses into a disabling one; this is particularly worrisome for people in jobs with manual labour elements. Additionally, ICBC will generally pay out a lesser settlement earlier on. The simple reason is that they are not going to pay you for a long term injury or disability until a significant amount of proof has been provided towards that result and they will generally operate under the assumption that people will get better over time.
Obviously, there are competing interests here. Although a better settlement/award is preferable, it can often be best to have a slightly lesser amount of money earlier. For example it may be preferable to have $17,000 now as opposed to $20,000 two years from now. Economic constraints may also force injured parties to settle earlier. The best way to avoid this situation is to seek alternative sources of income (see my previous posting on this), including: TTD payments, disability payments, and EI payments. A loan, particularly one from a third party, should be a last resort. These typically have relatively high interest rates.
For more serious injuries, it may be necessary to bring a case to trial (or the eve of) in order to get a fair settlement. This is not a hard and fast rule, however. Various other factors such as policy limits should be taken into account. As such, it is always important to discuss your case with an experience personal injury lawyer. The unfortunate truth is that the legal process is generally not a quick one. An experienced lawyer will, however, be able to identify cases that are appropriate to settle early on in the legal and insurance process.
