Sometimes it's about saving money and time, sometimes about making the walk more interesting. In the first category, we climbed Mayar and Driesh from Glen Isla, Ben Chonzie from Loch Tay, Ben Avon from Tomintoul. In the second one, for example Meall Garbh and Meall Greigh from Glen Lyon, Carn a'Choire Bhoidheach and Carn an t-Sagairt Mor from Callater side or Meall a'Chrathaich from Corrimony. These are not unique routes, just less popular. It's good to do something different from time to time
Also, less popular approaches are more likely to be quiet. I remember arriving on the summit of Chonzie, after walking in from Altdarnaig on a hot Saturday. The top was so crowded we couldn't find a rock to sit on
, but we hardly saw a soul on the way up.