[ndriscoll]

As long as it has decent IOPS, that should be fine? 100 MB/s is 5x UHD Blu-ray for example.

For something like a decent camera, you need more, but I'd expect phones would be fine. Most of the apps I have on my phone are in the 15-30 MB range, so a couple hundred ms if you had to read the whole thing to load. Seems reasonable to blame the app if it's slow.

With more space, you could also e.g. keep all of Wikipedia and all of your music on your phone, which will obviously be much faster than web services.

[The_Colonel]

SD card speed is fine for photos, video, music, movies and such, but potentially bad for e. g. apps where you need a lot of random access. You can certainly use SD cards effectively, but you need some knowledge.