These days, Macs get a little faster with new models. But a new computer is expensive and yet even Macs that are relatively old can benefit from an upgrade, such as memory or a fast SSD.
For example, if stuck with a 256GB or 512GB SSD, the MacBook Pro Retina or MacBook Air can get a 1TB SSD upgrade. Many other similar upgrades exist.
OWC has a large variety of upgrades for all Macs.