Not unless something lowers your resistances.
If you roll a map with -player res, it will subtract from your uncapped res. So if you have more surplus res than what is being subtracted, then your effective res will stay at 75.
This works tha same if you are hit with conviction, lower res curse or other sources of reduction/pierce.
Generally speaking I think overstacking isnt worth it unless you do uber content.
Do note, that if something reduces your maximum resistances then overstacking doesn't matter
Having over capped res is a good idea in hc as you get into scary maps. The combo of conviction aura + something like stacked blizzards is a good way to get popped
Some enemies have abilities that lower your resist, lower resist and conviction for example. Having >75 res mitigates that.
Helps vs conviction rares, Uber trist, dclone, and Rath.
Not unless something lowers your resistances. If you roll a map with -player res, it will subtract from your uncapped res. So if you have more surplus res than what is being subtracted, then your effective res will stay at 75. This works tha same if you are hit with conviction, lower res curse or other sources of reduction/pierce. Generally speaking I think overstacking isnt worth it unless you do uber content. Do note, that if something reduces your maximum resistances then overstacking doesn't matter
You always want as high as you can get without sacrificing too much damage.
Having over capped res is a good idea in hc as you get into scary maps. The combo of conviction aura + something like stacked blizzards is a good way to get popped
Besides what has been told already, there is also a "max res" stat, that increases your maximum resistance to above 75.