Laser systems typically come with a warranty on the laser system itself, including all parts. However, it’s never a bad idea to have a few replacement parts on hand, such as an extra lens and perhaps an X-axis belt.
Lenses can crack or break if they are not cleaned properly or if the laser is engraving/cutting while it is not properly focused. The X-axis parts control the side-to-side engraving motion of the laser. After extended periods of continuous use at high speeds, these parts can begin to wear and tear. For this reason, having a spare belt on hand helps ensure you’re never down for long.
Some users opt to create a “maintenance budget” where they set aside a certain amount from every job and put that money away specifically for future parts costs.