The IPID is a relatively recent thing. It became a requirement under insurance regulations and the idea behind it was to give consumers a quick, comparable snapshot of any policy before they committed to buying it, without having to wade through the full policy booklet to understand the basics.
Every pet insurance IPID should cover the same broad areas: what's included, what's excluded, where the cover applies geographically, how to make a claim and how to cancel. Because the format is standardised, in theory you should be able to compare the IPID from one insurer with the IPID from another and get a fair like for like picture.
In practice they vary more than you'd hope in how useful they actually are. Some are genuinely clear and well written. Others manage to be technically compliant while still being quite difficult to extract useful information from. They're a starting point rather than the whole story.
The key thing to remember is that the IPID is a summary. It is not the policy. If there's something specific you want to know, whether a particular condition would be covered, how an excess works in a specific scenario, what happens at renewal, the full policy booklet is where you'll find the detail. The IPID tells you the shape of the cover. The policy booklet tells you the substance.
"The IPID tells you the shape of the cover. The policy booklet tells you the substance."
If you're comparing policies and you can only face reading one document per insurer, start with the IPID. But don't make a final decision based on it alone, particularly for anything involving a pet with a health history or a breed with known conditions.