When a Mortgage is involved, the lender will want to ensure that the property to be purchased has sufficient value and is in a reasonable state of repair in order to stand as surety against the loan to the borrower. (It's no good finding out once the borrower defaults, that the �500,000 you lent as a mortgage was for a garden shed worth �500)
In other words, it is to protect the lenders interest, and the minimum they will require is a "property inspection and valuation"
Where no mortgage is involved, it is in the (cash) purchaser's interest that the house is in good order, in order to protect his own investment. According to the type / age of the property, it may require a Full Stuctural Survey to ensure that the property is not about to fall down or require major repairs.