When there is no audio transport you can use arrow keys to flexibly move the cursor. You can also flexibly create/adjust selections using the CTRL and/or SHIFT modifiers with arrow keys. 

Unfortunately these shortcuts do not work when playing or recording. LEFT and RIGHT arrow are used to seek during standard playback. The only keyboard adjustment you can make is to use the [ or ] shortcuts respectively to set the left or right boundary of the selection at the playback or recording position. The mouse can be used during recording and standard playback to arbitrarily modify the cursor or selection, but not during scrub play because the left mouse button is used to scrub-seek.        

A simple solution (at least for users of English keyboards) would be to have LEFT and RIGHT arrow adjust cursor and selection when playing/scrub playing/recording, instead of making those shortcuts do the same playback seek action as comma and period do.