"Saying some ppl 3bet and I 4bet is my thing" - perhaps you'd like to direct me to the time of the video where I said that so that I can elaborate on the context because that statement alone sounds a little weird.

When you pick up AA or KK and you're facing a raise and then a 3bet when you have yet to act, we are usually going to want to 4bet and hopefully get all the money in pre flop when our hand is strongest (this is actually called a cold 4bet because we have yet to act).  To balance those spots, and not only be 4betting AA and KK, and in BvB or around the blinds spots lighter hands like AK and QQ/JJ.  We want to sometimes cold 4bet with a hand that we are not willing to go all in with: a bluff.  This is turn can cause our opponents to ship all in lighter over our cold 4bets in the future, knowing that we will fold sometimes, which will turn a bigger profit for our big hands like AA, KK, etc...Not to mention that you do acquire a lot of folds by cold 4betting in the right spots.

On top of this fact, it makes you more difficult to play against.  If you never cold 4bet bluff, and flat 3bets with all your monsters, say AQ+ and TT+.  You're giving the original pre flop raiser a good price to get in the pot and crack your obvious big hand.  And usually in these situations, one or both or your opponents have position on you which gives them an added advantage.  And if they don't have position, it would mean that EP opened, MP 3bet and you flatted OTB or the CO.  If you were holding AA, or even KK here, you might've missed out on stacking MP's QQ or AK because usually at FR, ppl's 3betting ranges in EP/MP are much stronger and heavily weighted towards hands that are willing to go AIPF.

This is just a base strategy and the reasoning behind it (to answer your question).   As you become more familiar with these spots and why we are cold 4betting certain hands, etc...  You can play around with the hands that you flat 3bets with and make cold 4bets with, and then vary with the frequencies of each action in different spots and positions.

There are many pros and cons to 4xing.  First off, I 4x at FR, and 3x at 6max because we are playing so much more junk at 6max.  You lose more when you fold to 3bet, yet your opponents have to invest more to make a 3bet.  It narrows opponents hand ranges and punishes calling with weaker holdings yet gives you less of a mathematical edge for blind stealing.  I like to play bigger pots as the pre flop aggressor, but to be honest, it's really just a question of style.

I choose to 4x, and I don't think it helps me or hurts me (unless there's SSers behind me).  It's something I've always done moving up the stakes to where I am now.  For the most part, I don't think it's really important to my game (for example post flop play being way more valuable), I will continue to do it until it hurts me because this is a style of play that works and that I enjoy.