if the group head is properly dialed in (regarding pre-infusion position/cam catch), it should stay in that position.
tightening the nut won't change the height of the top assembly.
too loose/too little of compression on the seal stack= water/steam bypass, leaking.
too tight/too much compression= piston won't travel freely, it rather stick-slips.
you have to find, by try and err, a position in between.

my Gaggia Orione is ON 24/7 for 9-10 months/year; the v-lip seals last approximately 12-18 months before they start to leak.
the deterioration is more due to the heat exposure, which hardens the rubber, than the mechanical impact.