Ok here is hopefully an easy one… Why do some people boil for 90 and some for 60 min? I have been brewing now for a while and never have boiled longer than 60. How do longer boils affect the final outcome?
If you are brewing something like a pilsner or other light beer it is to drive off DMS. It can also be for hop utilization.
I’ve done a few batches where I only boil for 30-40 minutes, I usually do a first wort hopping or up the hops to get the IBUs for the shortened boil. I’ve only done this with amber and brown ales, like steelheader posted, a long boil on a delicate beer like a pils is to drive off DMS precursors.
here’s a dumb question what are DMS?
Dimethyl sulfide, it can give your beer a buttery corn flavor especially in light beers that use a lot of pils malt. A longer boil and quick cooling to below 140° helps reduce it. Here’s a good read on it.
I do a 90 minute boil for all my beers, 120 minutes with strong beers, but still use 60 minute hop schedules. I’ve found my beers to be more savory and complex with the longer boil. After a while superstition sets in and I just do it that way because that’s what I did last time. 
One other thing is that this only applies to all-grain brewing. Pils DME or LME doesn’t need a 90min boil, the precursors are removed during the drying process if I’m not mistaken.
I agree that a longer boil can change the looks (longer= darker) and character of your beer. I boil longer on things like a Scottish 70/- that I want more caramel flavors from. Thats in addition to boiling a gallon way down and adding it back. And of course longer boils convert more of your hop acids to bitterness so you can use less hops.
