It is not at all uncommon for me to receive an agreement of purchase and sale that is not initialled on each page. While there is no legal requirement that each page be initialled, and the contract can still be valid, it is still important to initial each page.
Having your initials, and the initials of the other party, on each page means that everyone has seen that page and has agreed to it. If anyone claims later that they were unaware of certain terms, it is harder to prove that they knew if they didn’t initial that page. Putting your initials down, and making sure they do too, gives you that added protection.