Let's talk platoons.
Like last year, the Tampa Bay Rays plan to use a platoon in right field. Last year, names like Eric Hinske, Gabe Gross, Jonny Gomes, and Rocco Baldelli were present. This year, Gross, Gabe Kapler, and Matt Joyce seem like the most likely to man right.
Kapler is the lone right-handed hitter, and the one assured of a steady gig. Throughout his career Kapler hits lefties at a .294/.344/.484 or a .828 OPS despite only seeing a little less than a third of his career plate appearances come against the opposite hand. Against the same hand Kapler has an OPS of .725.
Let's say Gross sticks on the roster long enough to gain a few hundred plate appearances. Last year the Rays did an excellent job of limiting Gross' exposure to lefties. In fact, only 21% of his plate appearances came against the same hand. Gross has a career OPS of .786 versus righties and .519 versus lefties.
This tells us that while Gross and Kapler should primarily be used in a strict platoon, there is room for overlap, at least against right-handed pitchers. Look at how Baldelli (61% of his PA came against lefties) and Gomes (64% against lefties) were used to gage how Joe Maddon likes to play the match-ups. There are some variables we're not going to account for here, pitcher splits and leverage of these events come to mind, but here are the main points to take from it all:
A. Gross will rarely see a southpaw.
B. Kapler will see mostly lefties, but can survive versus righties.
Just like that, the Rays have defeated the idea of using a lefty reliever primarily against Gross. Let's assume the duo combine for 700 plate appearances and that Gross sees most of the playing time, about 60%, or nearly 400 plate appearances, and hits for his career average against lefties and righties while seeing 80% righties. Kapler, meanwhile, sees 60% lefties.
Using a league average wOBA of .330, Gross would be worth -1 run overall if he sees 20% leties and Kapler worth 4 runs if he sees 60% lefties. Increase both numbers as you see fit, but the per plate appearance run value for Kapler versus righties is -0.006 while Gross versus lefties results in -0.08 runs. Quite the difference.
All combined, that's about three offensive runs over 700 plate appearances. Take away the 7.5 positional adjustment, add in ~10-15 defensive runs, and 22.5 playing time adjustment. Do the math and you get 28 runs, or about a three win player, only in the form of two players. Of course, this is not damning nor suggesting the Gabe of the day platoon will result in three wins, some possible alternations include less/more playing time based on injury or performance that alters from the career paths.
Given the security the Rays have at other positions they can certainly afford to play the Gabe game until deeming Joyce ready.
(Note: I'm well aware the Gabes combining for 700 PA is unlikely, but the exact number is rather irrelevant. The point is, that over a full season, when properly used, they will combine to be an above average player.)