You have continually marketed your property so you should not need a HIPs. However, after a period of time that the property is on the market and does not sell you will have to obtain a HIP. Your estae agent should know the details of this. You may find more information on the CLG website (HIPs).
The HIP will benefit you in selling your house because all the searches will have been done prior to selling and thus resolving any problems beforehand. This will therefore avoid any risk of buyers pulling out of a purchase on discovering any problems from the searches - everyone's a winner - no more costs incurred to any body.
Also in the HIPs is a mandatory Energy Performance Certicate giving ratings and recommendations to the energy effeciency of your house (rather like the rating you get on a frige). There is also a voluntary Home Condition Report which is a objective survey of the condition of the different elements of the building. This will tell a prospective buyer all he/she needs to know about the condition of the property. Since only about 20% of buyers pay out for a full survey (not the same as a valuation survey by the mortgae company) this report within the HIP and the HIP itself is an excellent idea and you perhaps should reflect on that when you come to purchase your next home.