It seems so logical, but unfortunately the importance is often underestimated. Homeowners often do not know it because they were never informed about it when purchasing the property or taking out insurance.
Not having documents in order can mean:
That you pay insurance premiums, but that you do not receive payment or only receive partial payment in the event of major damage
You may have problems obtaining a licence to renovate or to let your property
That if you are cut off for electricity or water you will not receive a new connection
That at Final de obra after a reforming you will be told that you must demolish buildings, for which no permit had previously been requested (note, also the time-barred / tolerated buildings!)
That the (holiday) rental license in reality is not valid, which means that you are not insured in the event of damage or accident, and that you actually rent illegally and therefore run the risk of fines (note, they are high!)
That you may have problems selling your property or it may be even impossible to sell