more specifically, here, the MOD approach is useful for handling scenarios where you have only Time values (as opposed to DateTime) and where said times may cross midnight

the main advantage is that the MOD(end-start,1) will always return the correct answer without need for manipulation of source values, e.g:

where end > start

=MOD("12:00"-"06:00",1) --> MOD( 0.25 , 1) --> 0.25

where end < start

=MOD("22:00"-"04:00",1) --> MOD( -0.75 , 1) --> 0.25

so, this approach is the more succinct alternative to the traditional approach of:

=if(end<start,end+1,end)-start

HTH