It varies for me. I wouldnt consider myself real strict on any one exercise. Though I will often do some sets slow and strict and at different rep speeds to switch it up. For example, when I do barbell curls I may throw the weight up somewhat, and resist the negative. I like to train heavy, but I always make sure I anihilate the muscle I am training. So that is not sacrificed. Heavy weights keep me motivated and strong all around. On my bench presses, form tends to be pretty strict, just cuz Ive never taught myself to cheat or arch on that exercise. Something like deadlifts, Im not sure how you could cheat the movement, but you can surely use sloppy form which can lead to injury very easily. Im always switching it up though. For beginners Id reccomend strict form, this worked best for me in the beginning.