It's an unfortunate fact that you possibly won't notice the negative effects of riding a loaded bike until you start to go up hill. On the flat it just rolls and on the downs it can be a bonus, so long as you haven't gone mad ... It's the ups that become the concern. Bikepacking just like backpacking is synonymous with weight saving, the lighter your kit the less work you'll have to do on the hills. This should mean you'll get less tired so you should be able to ride faster and/or further.
Getting your lightweight kit together isn't always simple. There are lots of factors you have to consider and compromise is usually the name of the game ... this balancing act has to take into account cost, weight, performance, pack size and practicality amongst other things. It must be said that even if you have bottomless pockets and aren't afraid to use them it won't always mean you'll get the equipment best suited to your requirements ... as an example, the lightest bivvy bag in the world weighs less than 100g, costs more than anything else BUT it's not breathable, so regardless of how super lightweight it is I personally wouldn't even consider it.
When you are trying to select kit and lets be honest there's such a vast choice it can become bewildering, you need a starting point. For many of us this will be cost and everything else will have to fit in around it but another starting point could be weight. I've had a think and compiled a list of what I would consider to be MAXIMUM weights for various items I'd take on a SUMMER over night trip. Obviously there's stuff out there that weighs much less but there's also plenty that's far heavier ... When I see a tent advertised as, ideal for backpacking with a weight of 3.5kg or a sleeping bag described as lightweight even though it weighs 2kg I have to wonder what type of medication certain members of the outdoor retail world are taking.
How much do you want to carry to the top?
• Sleeping bag - 1kg
• Bivvy bag - 500g
• Tarp (inc pegs/guys) - 600g
• Sleeping mat - 500g
• Stove and fuel - 200g
• Mug/cup/pan - 200g
• Groundsheet - 200g
• Evening insulating layer - 500g
Remember those weights are MAX so if I was looking for kit and the item in question weighed more but didn't offer me a significant increase in performance then I'd start to look elsewhere. Your biggest potential weight savings are likely to come from the above list. Also, remember it's not really worth buying that titanium spork if your sleeping bag weighs 2kg and packs to the size of a small country and those ultralight tent pegs won't have much of a noticeable effect if your tarp weighs 1.5kg.