only if the Y ticket is priced through the roof and there is an open award seat. like I won't spend 11K miles BOM-DEL if seat is available for 5K INR or so. But on BOM-UDR, where prices are generally higher, i would, if the price of a rev ticket is out of whack.
once on DEL - CCU, Y was full and not award availability , the cheapest other fare was 11k inr.. so used 18600 miles to book del - ccu in premiere with inr 700 as taxes.. online fare for this was 28k..