I can argue either side of the fence on this
Virtually every live mtt I play now (or did play pre COVID) is a re-entry. Many have add-ons. Few are freeze outs.
I don't think it's worth registering before the add-on with less than around 75BB. If there's half an hour before the add-on break, just wait for that and buy in for max.
Same goes if you bust early - if you're allowed to reenter at the addon point then wait for that - (note: if you're not allowed to reenter at the addon point, then don't even reg until addon).
But if you have an edge vv field deep stacked then by all means try to run up a stack early.
If any event has a bonus add-on structure (we have some $550 entry for 20K chips and $200 addon for another 20K chips) then i'd highly recommend buying in for your first entry at the add-on stage every time. Who wants to pay $0.2166 a chip for 60K chips when you can pay $0.1875 a chip for 40K chips? Instant >$EV.
Ofc if you feel like playing then by all means play - sometimes we're there and we'd lose more if we sat on blackjack for two hours