side marker lights and signal lights are two different thing
for one, in malaysia, how many cars has these side marker lights
this debate will be similiar to whether a not it is correct to on hazard light when it is raining and thus very subjective
from my point of view,
keeping the signal light on at all times is kinda dangerous
as humans, we normally give a short glance on certain things
many may not realise it, but when we see another car's signal, we normally take a very short glance and our brains will translate the message to us that the car ones to change lane
however, in that short moment, we sometimes fail to see that the signal light is on at all times and not blinking, thus causing our brain to mistranslate these signals
and from wrong judgement, we as driver will take into defence (well, most normal non-aggresive drivers do) and make way for the other car to turn into our lane