Part of it is my tendency to sit down with a file and start to type away, but long-hand, for a time, I was doing scenes. Which I found had its awkward aspects. Leaving aside the way that tangents and subplots tend to grow, and early bit characters or even objects tend to assert themselves and take a larger role -- writing in order gives it problems sometimes about needing earlier foreshadowing or setup -- there is the little aspect of keeping track of what you have written. Not writing the same scene twice. And then organizing them all into the final manuscript. Writing them without the connective tissue means it can be very hard indeed to graft on.
Organizing one that I did before I started to do longhand from front to end brings this all to mind.