I don't think anyone is saying only switch up your grip when you max. Who said that? Who said anyting about doing 1RM's (pr's or not) with over/over? I really feel no need to get in yet another post on this, lol, except I do feel the need to make clear what I (and IK) am saying and not saying. It seems like everytime I or anyone else says use over/over until you need to switch, someone comes along and puts words in our mouths, turing it into "only use over/under when you max". Couldn't be further from the truth.
I have NEVER, EVER not lifted a weight because of over/over. I would be using over/under. There is not sacrifice. If I didn't do it this way, though, there would be many occasions where I failed USING over/under. Becasue I DO have to work to keep my grip up with my dead weights. And I don't want to have to resort to a hook grip. Yes, I have used straps when needed, as well.
With deadlift dedicated training you can run into plenty of circumstances where your grip will be failing and you will be switching to over/under and therefore getting plenty of practice using over/under. Rack pulls for instance especially when rack pulls may mean something in the 6 rep range depending on your training needs and style.
Snatch grip deads, although ligher can challenge the grip since more of the pressure tends to be diverted to the weaker fingers.
Say you are are doing some high rep romanians. This may not be something you ALWAYS do in your training and your purpose, perhaps, may be to train lower back endurance, etc. I'll let the reader define "high reps" for himself
. So while you may be able to hold onto very heavy weights for a couple weights with over/over this doesn't mean you will have the endurance for this...thus another occasion where you may find yourself switching to over/under.
Also maximal training for one person is not necessarily the same for another. In my regular maximal deadlift training I'm having lots of occasion to be switching to and stayting proficient with over/under when I am doing "near maximal" or what some referr to as "circa-maximal" training. Which may be lots of singles at above 90% or doubles or triples. I'm not just talking about using over/under when you peak and do a 1RM..going for a PR or what have you.
For instance when doing singles I am working up to my best single FOR THAT DAY. That may or may not be a pr. Then I am accumulating single to hit a certain number depending where I am at in my plan. There is going to be plenty of occasion where I am using over/under for heavy lifts on those occasions.
These are just examples, there are many more. For myself I have always trained over/over until I NEED to switch, whenever that may be, and I feel completely comfortable with either way of gripping.
Flexing the elbows during deadlifting is a habit people often have PERIOD. Whatever the grip. I can see the logic, however, that if the bicep is put into a more favorable postion to exert pull, a greater potential for injury might exist. I don't know if that is true and I've never injured my arms at all deadlfifting but that doesn't mean anything. Certainly if you tend to flex at the elbows during deads, STOP! It's a very bad habit.