There are a few reasons for this recommendation:
1) The kitchen is the heartbeat of the home, and the benefits of decluttering will be noticed immediately
2) Functionality can be significantly improved by removing unneeded items in the kitchen
3) There (usually) isn't very much sentimentality or emotional attachment to kitchen implements
Find a way to touch each and every item as you decide what stays and what goes. This can be done cabinet by cabinet if you don't have room to empty every cabinet at once. If there are items you are unsure of, place them in a box and date it 6 months in the future. Then put the box somewhere out of the way, and if you haven't needed anything from the box by the date marked on it, you can safely assume you do not frequently need or use those items.
When you are finished decluttering, it is time to organize what remains. If you have reduced your kitchen supplies to what you truly need and use on a regular basis, there should be room for everything to have a place where it belongs - preferably close to where you use it.
TIP: As you're rearranging the items that will stay, try to keep your counters as empty as possible by finding space in your cabinets for small appliances. Clear counters have a serene look and are more inviting for cooking. Additionally, since clutter attracts clutter, keeping your counters clear will help prevent them from becoming a drop zone.