What does it mean to double dip? I’ve heard that term a few times, but still don’t understand exactly how it works?
A double dip is where you get a 2 for 1

For Chase it's a way to get two cards when you're technically only eligible for one, it's taking advantage of a poor system design loophole. Some people are comfortable bending the rules, and if you are and can take on the MSR, it can increase your points earnings. There's a write up of how to do it now on DISchurners as it's slightly different now than when I did it last year.
I used it to get both Sapphire cards after the One-Sapphire rule was introduced. Some use it to get 2 Southwest personal cards after the same rule applied there. But I think most people use it to get 2 cards on their last 4/24 slot. Since you have to be under 5/24 to get a Chase card, when you go for that last Chase card you can actually get a 6th card at the same time if you do a modified version of a double dip.
This all makes sense. I guess where I get confused is won’t I eventually have too much debt for my income and will either be denied new applications or have to request my CL be reduced?
We do not carry balances. We pay in full each month, even with our CIU, which has a 0%. Does it hurt our credit to request a credit reduction? We have way more than we could ever possibly use.
Ok so a distinction on terminology, debt is the actual amount of money you owe to a creditor at any given time. In terms of your credit score, mostly that's looking at debt to credit available to determine a utilization score - how much of your potential debt (aka. available credit/credit limit) are you using right now - and not necessarily comparing it to income.
Credit issuers are usually looking at your CL with them and comparing that to your income as an internal risk assessment. Using that in conjunction with your credit score, they play a 'what if' game to determine the potential for losses, i.e. you run bills up to your CL and then default, how much would they stand to lose if that happened? When we discussed keeping your available credit to reported income ratio less than 50% with Chase, that's what we're trying to mitigate.
So you want to strike a balance between keeping a high enough overall credit limits to keep your utilization numbers low, but don't necessarily want high CL's with individual issuers to keep a low risk profile at each issuer. If you weren't ever going to open more credit lines with Chase, it wouldn't matter what your existing lines are now, they've done their risk assessment and are happy with what they gave you. But if you seek additional credit, then they have to reevaluate and you might be deemed too risky at that point. In an effort to appear low risk, you could decrease the limits on the cards you're not using to open up room for credit on newer cards.
That said, at a certain point even having high credit limits across all issuers can start to look risky. Tagging
@SouthFayetteFan here as I recall with his game, he and his wife were showing several times HHI in open credit lines and reduced those to present a better risk profile to creditors (to keep playing the game!). Perhaps he can share a better evaluation. Despite having double digit revolving credit lines open, I'm not at that point yet
Thank you! This is exactly what we were thinking. We were concerned with spreading ourselves too thin, but also wanted more flexibility—as you mentioned. Just out of curiosity, between IHG or Marriott, which brand do you feel has offered the better deals? I ask only because I am a Hilton Honors Member and have used points a couple times, but found it was much more difficult to have the number of points needed to secure multiple stays. We have IHG rewards as well, but also never managed to build up enough points to use them. That said, Marriott is the only hotel card we’ve ever taken out where we received a MSR.
That is so tough to answer right now

Historically I found IHG easier to rack up points but they've changed up how they do the Accelerate programs and I'm not able to get the same bang out of a buck with that. I find they are usually lower costs than Marriott, but not always. Marriott definitely has the slightly better footprint now and a range of properties with lower price points so in the last year we've switched to Marriott's and Hilton's, as they just happened to work out with a deal or promotion to edge out IHG. Both Hilton and Marriott being part of AmEx swung to their favor with the AmEx offers coming out. There's some offers for Kimpton through AmEx but we tend to stay either HI or HIE's, around that level versus Kimpton and Intercontinental levels.
But what solidified our points balances with all of them was picking up a CC card with a high sign up bonus. I picked up the IHG when it was 80k points (kick myself for not knowing about the 100k offer way back when) and I think hubby got the Marriott at 80 or 100k around the same time. Through some work travel and switching up paid stays with points redemptions we've kept up those balances over the years. I still have some of my original 80k in the IHG balance

We did the same with the Hilton card, grabbed it at 100k with a statement credit and waived AF. That card is up to 125k now but the AF isn't waived so we didn't miss out on much. Now I just work to maintain the balances. My plan is to pick up a few more Hilton cards between the two of us (yay points pooling!!) because you need way more points to book Hilton's (but you can also earn a boatload with the credit cards) so I need a much bigger stash than I typically keep in other programs.