Fade-ins and fade-outs can be copy-pasted. Crossfades, currently, cannot.
If you plan to make a video that crossfades between lots of footage (for example, like a slideshow), and you’re unhappy with the default duration and style, you can’t change that without manually editing each crossfade.
It would also fulfill the use case if multiple crossfades could be selected and edited at once.
It’s entirely possible to set the duration of transitions globally.
It’s all explained in the documentation: Tips & Tricks → Tips & Tricks → Configuring the Default Transition Duration.
That’s true but you cannot change the composition type or wipe method. I think it would be great if you could define several presets for the crossfade / same-track-transition, set one as the default for double-clicking the cut, and have the list of presets available when using the icon in the timeline toolbar.