last season in the nba if you played two team parlay round robins with all dogs every day you would have won ~430 units. There were some stretches were you would lose 100 or 200 units in a week or two (when favorites cashed regularly) and others were you would win that much, but yeah. VERY streaky. I didn't look back any further than that as I haven't bet in over 2 months and I was looking at it when I quit.
Keep in mind if there is a full slate of games the total number of parlays is, I think, 150 or 136. So, if you normally bet $100/game, you probably don't want to make $100 the unit size.