With the average UPVC door they DO need to be locked from inside !
"errm, virtually all doors these days don't need locking to be secure. You need to key to open them from the outside, to get out from the inside, just push the handle."
With the average UPVC door they do !!
if you don't want your house broken into + car stolen !
Very common for a large bent lever to be pushed thru the letter box to apply downward pressure on the handle - Bingo ! door open, car keys usually on the hook by the door