The Phillies swapped out backup catchers, a side effect of trading for reliever Brad Lincoln. By itself, the transition from Erik Kratz to Wil Nieves backing up Carlos Ruiz reads as follows.
Wil Nieves, 36 years old
.297/.320/.369 in 71 games (2013), .242/.283/.314 in 385 games (career)
rSB: -2 (2013), -4 (career)
RPP: -2.7 (2013), -1.3 (career)
WAR: -0.3 (2013), -2.6 (career)
2013 salary: $800,000
Erik Kratz, 33 years old
.213/.280/.386 in 68 games, .220/.281/.407 in 129 games (career)
rSB: -2 (2013), 3 (career)
RPP: 2.2 (2013), 2.2 (career)
WAR: -0.3 (2013), 0.9 (career)
2013 salary: $496,000
On the rSB (runs saved by throwing out base stealers/preventing steal attempts) and RPP (how adept a catcher is at blocking pitches) scales, for which 5 would be elite and -5 would be awful, all of Nieves' career numbers have minus signs in front of them. His blast of fortunate offense the past two seasons, which in his minimal on-field time has seen him flirt with .300 twice, is not enough to outrun this.
Nieves was signed as a "defensive" catcher, an aspect that gave him the edge while battling Rod Barajas for the backup role with Arizona last spring. He got plenty of starts (71) due to Miguel Montero's lingering back issues, and while his batting average kept going up, his OPS hibernated below .700, meaning his slugging power and walks were not at ideal levels for someone who hits .300 more habitually. And here's what AZ Snake Pit had to say in regards to Nieves' highly cited defense (bold mine):
"What was perhaps surprising is the defensive numbers for Wil weren't all that good either. 13 out of 18 stolen-base attempts against Nieves were successful, a 72% rate (admittedly, still likely better than Barajas would have managed), and in 380.2 innings of work, Nieves allowed a remarkable 33 wild pitches. Every other NL catcher with that many WPs, had at least 900 innings behind the dish; it was also the most wild pitches by any major-league catcher with less than 500 innings played there, since Sandy Martinez with the 1995 Blue Jays (he allowed 38 during his 472.2 innings)."
By comparison, Kratz allowed 16 wild pitches in 478.1 innings, but 79 percent of his base stealers were successful. The bar was low, and each guy has his faults. This was clearly an area where Ruben Amaro Jr. felt he could risk moving backward, while moving forward elsewhere - in the bullpen, with Brad Lincoln (hopefully).
Nieves will likely get 30-40 games of work, barring some other cataclysm, so it will be a limited effect he has anyway.