I’ve created a page rule for a certain url and turn waf on in that page rule. My waf under manages rules is currently off. Do i need to turn it on?
If using some Paid plan like Cloudflare Pro Plan, you have an option Web Application Firewall under Page Rules to either enable or disable for specific Page Rule when needed.
You can have WAF turned on (enabled) for general use while also having it turned off (disabled) using a Page Rule for specific reason.
From my point of view, it is really beneficial and a good option and I would recommend you to have it enabled and selected the needed WAF rules (like WordPress, PHP, etc.) for better security and protection of your Website (domain) and if possible in some other combination with like custom Firewall Rules, or Hotlink protection, Bot management, etc.
More about securtiy options can be found on the below article:
Create a page rule