On MTBs, 2x is slightly easier to keep adjusted and affords more tire clearance. On many bikes, going bigger than 2.1 will result in the knobbies buzzing on the tail of the FD cage. Problem increased with 27.5 and 29" tires.
1x is becoming more and more prevalent also.
They're only lighter with the more expensive cassettes. $75-100 cassettes with 46t+ big cogs pretty much outwegh a front shifter and derailleur.
Last edited by LesterOfPuppets; 01-06-19 at 06:39 AM.