Only you know how much your time/money is worth to you.

For me, if i was taking a long vacation to SIN and it was 4 hours and $200 to add on PRG->HEL and HAN->SIN (or whatever) so that I could take advantage of a good J fare (assuming you wouldnt be able to fly J if you booked PRG->SIN).

If i was traveling NYC to LAX for a long weekend I dont think i'd book NYC->MSP->LAX to take advantage of a cheap F fare if i could get a reasonable Y JFK->LAX.

Recently I used Delta miles to go to Brazil. Wanted to fly JFK->ATL->GIG in J. Managed to save 80,000 miles per person by flying HPN->ATL->GRU. The drive to HPN was 30 minutes longer and $40 more than getting to JFK and I was able to buy a GRU->GIG flight for $40 per person. So an extra $120 and ~3 hours to save 160,000 miles. Worth it.