I hold my hit in for a few seconds only because it feels more natural to me and I like it, but I do not delude myself thinking it makes me any higher. Kinda the same for massive clouds.
Yes clouds are important! It shows the extraction efficiency of the vape in session. Maximum hold time in the lungs should be no longer than 7 seconds. No matter the temperature you are Vape'n, it's just better for the lungs.