Pressure welding forces the cross bar into the bearing bar under heat and pressure, so the joint becomes part of both bars. It is fast, strong and the standard answer for load-bearing panels in carbon steel.

Press locking slots the bars into each other and drives the joint home mechanically. There is no heat, no weld bead and no discolouration, and the surface is the same material everywhere on the panel.

In carbon steel that difference is mostly cosmetic, because galvanizing covers the joint either way. In stainless it is not: welding heat affects the surface around every joint, which is both an appearance question and a corrosion one, since the heat-affected zone is where stainless is most vulnerable.

The practical rule is welded for load-bearing carbon steel work, press locked for stainless and for anywhere the panel is visible or washed down frequently. Where both would work, the decision is appearance and price.