With unemployment so high, many people are just excited to get an offer for work. After months and months of searching, it's easy to want to scream, "Yes, I'll take it!" when the first offer comes along. But before you pull that trigger and pack your lunch, make sure you get everything you need in writing. Often, that takes the form of a job offer letter.
If you have an actual contract, it's likely many of these terms will be addressed. If you're not working under contract (union, or otherwise), this letter is the only proof of certain rights and privileges you might get. If there are certain exceptions to company policy that your hiring manager may have promised verbally, get it in writing.