They literally take a burden off your feet. Sturdy, flexible, and comfortable, they are perfect for hiking and most backpacking. Welts are stitching systems that join boot to sole. The better the welts, the stronger the join. Hence welts make shoes that are more water-tight, more durable, though perhaps less flexible.
Lighter shoes use bonding-cement joins.
Get it right. You and your hiking mates will regret it if you don't. Seek out a reputable store and an experienced salesperson to find the best fit . Unless you're replacing a specific size and model, exercise extreme care with mail order purchases or discount-mall shopping. There are too many variations in the human foot and body to take chances.