That's the main reason I did it too (on my 2nd and 3rd Rocksters anyway, after that it just became a habit...). Doing a 110mile round journey every day - I was trying to use the cheapest fuel on that route I could, but the standard range can't "quite" make it a 2-day event, I ended up filling every day, which was tedious as hell. Adding about 30 miles of range (ish) meant I
could fill up every other day instead.

IIRC the Rockster tank goes on to reserve at about 145 miles normally, (and there's 45 miles in that reserve) but with the mod - the reserve light comes on at about 165/170 miles instead, with 98RON and gentle, efficient riding I've even seen it come on at 205 miles.....