what is butt joint in welding

3.Stitch welding
Talking about the stitch welding, as the name indicates the welding is done in a stitching manner.just see the pic, they are used for connecting long welds where continues welds are not needed, it's simply implemented to reduce the cost of welding

And about fillet welding they are used for welding pipes and welding cross sections of infrastructure, and when fastening metal by bolts isn't strong enough and wear off easily