There are several approved alternate fuel planning methods. One of them if something like 12 conditions are met they can plan to not have an alt.
The different methods and rules for each one cover about 8-10 pages in part A fuel planning.
Its legal and if your MTOW or MLW when you arrive you really don't have much choice but to use it.
Are we happy using it.... not really... Will we take extra if we can.... hell yes.
But as its legal and no other safety issues outstanding, If you refused to accept the flight plan and off load freight just to have alt fuel you would be having a chat with someone.
Valid safety issue wx, historical expected traffic level etc not a problem asking to either recalculate with an alt and off load freight. But most if not all company's these days have huge databases with historical fuel burns including time of year and wx and its pretty accurate.
How much fuel does it save and hence money.... colossal amounts over a year we are told.....