Cutting capacity is usually described in terms of clean cut and maximum cut thickness, and the two are worth distinguishing. Clean cut is the thickness a machine handles with a good edge finish and reasonable speed, while maximum cut is the thickest material the machine will get through at all, usually slower and with a rougher edge. Buying with your typical material thickness in mind, rather than the thickest job you might occasionally face, generally gives a better day-to-day result.
Space and power supply are the other two practical constraints worth checking early. Confirming that a chosen machine will run comfortably from the electrical supply actually available in the workshop, and that there's room to work safely around it with materials laid out, avoids the common mistake of buying a machine that then can't be used the way it was intended.
Our own TP Weld Tables range is designed and manufactured in-house in Yorkshire, cut on a fibre laser for tight tolerances, which is the kind of detail worth asking about wherever you're sourcing a table, and you can see the full range via https://google-pluft.nl/forums/viewtopic.php?id=245929.
Portability and power supply matter as much as the process itself. A stick welder will run from a generator or a domestic supply in places a gas bottle can't easily follow, while MIG and TIG set-ups need a gas cylinder and, for anything beyond light-gauge work, a heavier electrical supply. Workshop layout, the materials you weld most often, and how frequently the machine needs to travel are all worth weighing up before settling on one process.
Duty cycle is one of the most misunderstood figures on a welder's spec sheet, yet it tells you more about real-world usability than the headline amperage does. It's expressed as a percentage over a ten-minute period at a given output, so a machine rated at 30% duty cycle at its maximum amperage can run for three minutes out of every ten at that setting before it needs to rest and cool.
Where the extraction point sits relative to the arc makes a bigger difference than most people expect. A fixed overhead hood can miss fume entirely if the work moves around the shop, whereas a flexible arm or on-torch extraction follows the job and tends to capture more consistently. Filters also need regular checking and replacement; a clogged filter doesn't just reduce airflow, it can quietly reduce the whole system's effectiveness long before anyone notices.