Usually its easier to subtract numbers written vertically because of the sheer fact that you're just taking away instead of adding on. If you have basic idea about adding then you should understand subtracting easier. But, because most schools teach adding first its easier for some.
Yes it is, if you have a problem like 34,789 - 28,058 it would be much easier to put 28,058 under 34,789 and subtract it vertically rather than trying to subtract it mentally. Obviously subtracting numbers vertically only works with numbers with 2 digits or more.
