While they don’t work exactly the same as each other and serve slightly different purposes, the attach feature is often used in conjunction with welding, specifically in how many layers you can attach.  The attach feature works by keeping multiple layers attached to each other, however this can often cause problems when you have too many layers that are proving to be a little awkward to attach.  This is where you will need to use the welding tool to weld together the different shapes or letters that can then be attached as if they were one layer. For example, you wouldn’t be able to attach multiple different letters to another layer since there would be too many at once. However, if you were to weld the letters and make a single word, this would count as one layer and you would be able to then attach it far easier to another one.