You know what it is like, you wait 15 years for a Local Plan then 3 come along at once. This month Emsworth, Havant and Portsmouth all made progress on their local plans.
Why is it important – in theory, all local planning decisions are driven by the local plan. If an area needs a new doctors surgery before proposed housing can be added, expect this to be costed into Section 106 arrangements for the developer as part of any planning approval. Same for new roads and infrastructure.
Want to build something different – check the local plan – if it is not already within the definition of what can go into that area, it will never get approved.
If proposed government changes happen, you will not need planning permission anymore – if you propose something which is inline with the Local Plan, approval is automatic – so these Local Plans and their content are really important.