I just went down this journey myself last month, and it's a decision I have not regretted at all. Before I took the dive into going lighter in the entire bag, let me show you where I started from. I am a golf coach of 14 years, a former collegiate player, and scratch golfer still today. I live in the 110-112 mph range with driver, 92-90 mph with 7-iron, and I play X-flex shafts through the bag. Last summer I went 10 grams lighter in my fairway woods in the effort to improve launch and not hit bullets with them all the time. That's what started the wheels turning. Well, that and a lot of research through YouTube, TXG, and my go-to fitter here in Houston. At the time I was playing a 73 gram driver shaft in TX flex with low torque and a low launch and low spin profile. I had been in this very shaft for 15 years (senior year of college golf), and I just can't kick it out of my driver with the numbers I get no matter what driver head I play (currently a SIM @ 9* in standard position). I was also in KBS Tour 130 X iron shafts which were solid, but sometimes spinny out of the blue and a little more high launching than desired. My back-up set of blades have C-Taper 130 X in them. Anyway, the point is this: heading into the summer I started to notice the higher launch and spin spikes more and more. I also noticed a 5-yard drop in carry yardage in my irons. The driver hadn't changed much, but I would notice I was getting tired at the end of the round and struggling to finish with it. (Driving the ball is a big strength of my game).
I decided a month back to try a super light driver shaft. I wanted to leave no stone unturned, so I decided to drop 20 grams and go head first. I shelved my Fujikura Rombax 7Z08 - TX driver shaft for an Aldila Rogue Elite Blue 55-X. I also, dropped 10 grams in the iron shafts and moved from the KBS Tour 130 X to Nippon Modus 120 X (I left my KBS Tour 130 X wedge shafts alone bc I like the heavier feel there and get great spin and launch numbers from them - I never fit full wedges). Both decisions, driver and irons were exactly what was needed. Now, full disclaimer here, you will have to add head weight if you go lighter in the shaft. I added 7 grams to the driver head by changing the back weight, and the irons only needed a little lead tape here and there (they were previously married to 120-gram shafts before I put the 130s in them a while back, so no issues there). I just want you to know that swing weight has to be taken into account when dropping weight or you will spray it all over.
The results have been amazing for me. I picked up the missing 5 yards of carry in my irons again, plus about 3 more, and my launch lowered to the correct windows. I was able to just swing and not have to hit and work to produce the shot I wanted; my feel returned. With driver, I picked up about 3 mph of ball speed on the average. I went from 160 mph to a 163 mph average (I have touched 167 a few times lately - haven't been there since college, and I'm 37 in a few weeks). I had trouble with lower launch and spin at first, but that just helped me know where to adjust head weight to get the swing weight back in order. I did some lead tape experiments to get the weight where it was needed - when I verified I needed launch and spin, I just put all the weight as far back and low as possible. Thanks to Billy Bob's golf and the SIM design, I knew I could get the sliding weight and back weight combo that I needed. $40 well spent on those! New driver numbers have me at 163 mph ball speed, 2100-2400 spin, launching at 12-14* and my dispersion is even tighter than before. I am not hitting the driver anymore, but rather swinging it, and I am able to shape it from the tee again without fear of not being able to hit it as far as I want. It's the easiest 300 yards ever. I must note that my irons lost some spin too, but the spin lost has allowed me to not have to play such a firm, low spin ball anymore. I'm now able to play the softer tour balls with a little more spin and I'm really loving the softer feel all around. It has given me a new level of shot variety and spin control around the green (I've always had to play the low-spinning, x-model, tour balls), and I am loving the softer ball off the putter. It's also not as harsh off the club with the lower compression. All in all, I've dropped 20 grams in driver, 10 grams in fairway woods and irons, and I'm loving the results. I'm longer, more accurate, and have turned back the clock about 10 years on my game. I'm also not nearly as tired and can practice longer with less pain or recovery time. My body is thanking me as well - 24 years of competitive golf has taken its toll for sure.
All this to say:
1. lighter is faster and faster equals distance
2. you have to get the swing weight correct for you or you will spray it and be shorter from poor contact
3. verify everything with launch monitor numbers
4. do your research before you jump - knowing your numbers on the launch monitor before and what you want to fix, where you want to get to, what your current golf shafts are designed to do, and what the shaft you are looking to try is designed to do is so valuable - this will save you from wasting time and lots of $$$
5. ask questions to reputable club fitters and coaches who know your equipment and know equipment in general
these 5 guides will help you get it right quickly and without chasing a rabbit and wasting $$ - even then it can still be a tricky process. I took my time doing the research and made sure I started with a low-cost, older-model driver shaft from eBay just in case I didn't get everything right in my quest. Fortunately, that low-cost start nailed what I was trying to do, and it saved me a lot of money too.