Reality check by Mac generation
Apple Silicon (M1, M2, M3, M4 · 2020+): SSD is soldered to the logic board. NO upgrade possible without Apple-spec service (and even then, requires firmware re-pairing · usually fails). Buy the storage you'll need at purchase time.
Intel 2018-2019 (T2 Macs): SSD is removable (proprietary connector) but T2 chip binding means upgrade requires DFU restore + firmware pairing. Possible but specialised.
Intel 2015-2017 (no T2): SSD upgrade is straightforward via NVMe + adapter card or proprietary Apple SSD. Best upgrade target.
Intel MacBook Pro 2015-2017 SSD upgrade
The upgrade needs an adapter board (Sintech NGFF M.2 → Apple PCIe), an NVMe SSD (512GB, 1TB, or 2TB), plus fitting and macOS install — WhatsApp 0312-4690005 for a quote.
Total cost rises with capacity (512GB, 1TB, 2TB) — still excellent value vs buying a higher-storage Mac.
Intel MacBook Air 2015-2017 SSD upgrade
Air uses different SSD connector than Pro. NVMe via adapter is possible but compatibility varies, and cost depends on capacity. Some pre-2015 models max out at 1TB Apple-spec SSDs.
Intel 2018-2019 T2 Macs
Technically upgradable but requires Apple Configurator + another Mac to DFU restore. Specialised workshop work with labour above part cost. Often not worth it · better to sell + buy higher-storage M-series.
Apple Silicon storage workarounds
External Thunderbolt 3/4 SSD (1TB or 2TB Samsung T9): reads/writes at 2,800 MB/s · fast enough for most work including 4K video editing.
iCloud Drive: a monthly subscription for 2TB. Files-on-demand keeps the drive free, downloads on access.
External RAID NAS for studios: bigger investment but unlimited expandable storage.
Cost-benefit decision tree
Your Mac is 2015-2017 Pro + you need more space: SSD upgrade is worth it.
Your Mac is M-series + storage full: get a Thunderbolt SSD or upgrade to a higher-storage Mac via trade-in.
You're buying a new Mac: spec 1TB minimum unless you're certain your needs will stay under 256GB.