plone.app.mosaic provides a "Format" menu for tile where you configure e.g. the text alignment of the content within a tile. What is the particular usecase for that. In case of a RichText tile I would align the text according to my needs using the TinyMCE controls of the tile. Why is this needed? I understand that you need sometimes a formatting options for the row e.g. for the background color but the formatting of individual tiles should be left to the individual editing option of a particular tile, or?
Some history: In Deco all formatting actions were in top toolbar and Format-menu included also TinyMCE-actions (dedicated buttons were only created for ”favorite” actions). It was (and still is) possible to configure dedicated set of actions for every tile type. Once Mosaic users wanted regular TinyMCE with floating toolbar (with the default configuration), format menu was only left for non-TinyMCE actions. So, things were originally designed consistent, real usage required compromises, but redesign to restore consistency never happened.
Re-reading @zopyx's question I totally missed the detail about text alignment. So my answer above is probably not very useful. I most frequently use padding-bottom from the tile menu, very occasionally I'll use the float left and right.