I disagree, I like having the different size pots around, especially since smaller volumes of water in smaller pots tend to heat/boil faster. On brew day I typically use our regular 2qt stock pot, plus my old 16qt extract brew kettle, plus my 8.5 gallon turkey fryer. I can heat various kinds of water to different temps this way too.
It's true that some people would have uses for the other pots. Some in brewing, some for other things.
Lots of people don't have use for a 5 gallon pot if it's not their main boil pot though. Now if I could still eat oysters..... About 4 gallons of oyster stew would be a great use for it!
As for me, I've got extra pots now that I don't have much use for. I do use two though. I use my boil kettle for heating my mash water, then since I'm going to drain to the boil kettle I use another kettle for sparge water. I don't worry about the time to heat. Whatever pot I use and whatever amount of water, I can get to temperature fast. I went ahead and bought a very hot propane burner. I don't worry about sparge water until it's nearly time to drain the mash tun.
I do use one of the several smaller pots that I have in the kitchen to boil up and make a yeast starter and believe it or not I've used the five gallon pot to make top ramen.
My daughter was having a sleep over and let me tell you, a small mob of seven year old girls do like top ramen!
Ok so say if I do get a 10 gal pot... The recipe kit instructions say to do a partial boil. So would I be better off just doing a full boil? How could I convert it to full boil when it comes to hop utilization? Or, do I continue to follow the instructions and do a partial boil in the 10 gal pot?
If I were you, I would do everything exactly as the instructions say to get started. Then start changing one thing at a time.
I think the reason that they say to do a partial boil is because with say three gallons, you have plenty to dissolve the extract, plenty to extract the qualities of the hops you are after, and it takes less time to cool three gallons than it does five. If your top off water is cold, it takes even less time.
A couple other reasons for three gallons is probably the size pot that comes with most starter kits and you don't have to figure out how much water to start with so that after you loose water to steam, you end up with five gallons.
A three gallon boil isn't a bad idea until you get a chiller of some sort. You are going to want a chiller at some point in the near future if you start loving making beer. It saves time and the time saved is time that you are not exposing the beer to potential infections.