When Nate Schierholtz signed with the Cubs, he was coming off of two pretty identical seasons:
That was good enough to garner a 1-year, 2.25 million dollar contract. In 2012, he was strictly used as the dominant half of a platoon and it showed: Nate had an .826 OPS against righties but a putrid .444 against lefthanders. It's important to note that he only received 269 PA, though. His split in 2011 was similarly severe: he hit .801 against righthanders and .562 against southpaws (again, OPS). What's interesting about that harsh split is that it's a recent development, though. His career numbers are .739/.703, so the past two years have basically made the entirety of the difference.
When the Cubs signed him, they made sure to go out and get someone to hit lefties to platoon with him (Scott Hairston). This season, the goal with Nate is clear: start him against righties whenever possible, and spin him into long-term assets at the trade deadline (The Giants traded Schierholtz + at the deadline for Hunter Pence last year). We'll see whether or not that ends up happening, but the plan itself is sound.
As noted, Schierholtz has a harsh platoon in recent years. The last time he hit a HR of a lefthander was in 2009 (when he actually had a reverse platoon split). Generally speaking, though, Schierholtz is going to provide a .260/.320/.420 line from RF. That's the equivalent, funny enough, of a Hunter Pence or Will Venable. These aren't guys we would consider all-stars at RF, or even average; I'd agree with that consensus. Schierholtz, even when platooned correctly, just isn't an offensive force. His career ISO is .141; David DeJesus' last year was .140. He doesn't draw a considerable amount of walks; his 6.2% mark is firmly well below the MLB average of 8.5%.
Schierholtz makes contact at a rate higher than the average MLB player, but he also swings more often. This would normally have the unfortunate effect of abbreviating his P/PA; however, he fouls off a much greater percentage of balls than the average player (32% to 27%). This helps drive up P/PA: his last 3 full seasons have had marks of 3.87, 3.97, and 4.00, all higher than the MLB average of 3.81. Nate has a tendency to chase pitches out of the zone, but also swings at pitches inside the zone with a pretty great frequency (the average is around 62%; his average is around 70%). All of these things point to a guy who is likely not walking a lot or striking out a lot. This means, of course, that BABIP is the supreme arbiter of the quality of his seasons. He's looked good this year, but his BABIP has been .353.
Schierholtz enjoys hitting changeups and cut fastballs and that's about it. Pitchf/x rates him as essentially average or worse against every other pitch save the knuckler.
From most accounts, Nate is a good defensive right fielder. Fans rate him as having a strong, accurate arm, and he has shown a high UZR/150 in right over his career. Unfortunately, it doesn't look like he could play CF. he was tried there for a week or so last year and rated poorly (and I remember him not having the instincts or spped for it). Even if Nate is a strong defensive RF, it doesn't provide much in the sense of surplus value, due to both the relative unimportance of defense at the position and the fact there is very little room in RF for any venturing outfielder to make plays. For what it's worth, Schierholtz has an essentially average range factor at RF; this is the primary driver of his miniscule (but not negative) defensive value.
Nate Schierholtz was brought in by Hoyer to do one thing; hit right-handed pitching. There's no reason he shouldn't be able to do that with a passable level of success. If he can do that, he can be valuable. A $2.25 million dollar contract isn't a hindrance to any team, and to be a success he'd have to provide maybe a single WAR. He's already been worth 0.4 this season, the same mark as his output last season. Schierholtz stands to get 400 or so PA on the Cubs this year and I'd expect him to have a wOBA of .330 or so. That's a valuable piece at the trade deadline; maybe not as a primary offensive upgrade, but as a very serviceable injury replacement. All told, this is a low-risk, medium-reward move that a good GM should be proud to make.