Five winters ago, had a lugged steel custom bike built as my primary commuter. Before bike build, cleaned and brushed the internal tubing as far as I could reach - then gave the insides a good coat of Boeshield. Made sure it dripped out of the limber holes, also checked to make sure none were plugged. Plus put a second coat in the lower seat tube and bottom bracket area. This bike has been ridden thousands of km year around in just about ant imaginable weather. Late in the spring the bottom bracket needed replacement, while I doing this- also took the seat tube out to inspect for rust - found none. Put a new coat of Boeshield around bottom bracket area- then reassembled it. Not sure if the Boeshield really helped or not, perhaps it helped my sense of well-being. However my bike frame innards were pretty clean. Aside from additional expense, not sure there is a down side to doing it.