First, pragmatic approaches are guided by what Warmbrod calls a “requirement of minimalism”: … logical theory should be as simple, as modest in its assumptions, and as flexible as possible given the goal of providing a conceptual apparatus adequate for the project of systematization. In practice, the minimalist constraint dictates that the set of terms recognized as logical constants should be as small as possible (Warmbrod 1999:521). While pragmatic demarcations seek to minimize what counts as logic, principled demarcations are inclusive. They count as logical any notion (rule, system, etc.) that has the favored property. It is simply irrelevant whether a notion (rule, system) is required for a particular purpose: its logicality rests on features that it has independently of any use to which we might put it. MacFarlane, What does it mean to say that Logic is Formal?, p.16-17

The literature on demarcating logic contains examples of both general approaches (Principled: Kneale, Tarski, Dummett, Peacocke, Hacking, McCarthy, Sher, Dosen; Pragmatic: Harman, Tharp, Quine, Wagner, Shapiro, Warmbrod) and it is important to recognize three differences between them. MacFarlane, What does it mean to say that Logic is Formal?, p.16

First, it is useful to distinguish between two general strategies for demarcating logic. The first is to identify some favored property (formality, topic-neutrality, conservativeness of introduction and elimination rules, permutation invariance, etc.), or perhaps some combination of properties, as a necessary and sufficient condition for logicality. Call approaches like this principled demarcations. The second strategy is to start with a particular job - for example, to serve as a “framework for the deductive systematization of scientific theories”, or a framework for the characterization of structures - then find something that is capable of doing that job, and identify it as logic. Call approaches like this pragmatic demarcations. MacFarlane, What does it mean to say that Logic is Formal?, p.16

A second difference is that pragmatic approaches tend to be holistic, in a way that principled approaches usually are not. Since it is the whole logical system that does the job, systemic properties - decidability, completeness, compactness, the Lowenheim-Skolem property - play a greater role in pragmatic demarcations than local features of particular notions or inference rules (see Quine 1986 ch.5, Tharp 1975, Wagner 1987). Although nothing about the idea of a principled demarcation excludes appeal to systematic properties, principled demarcations tend to appeal to local properties of particular notions or inference rules (e.g. topic-neutrality, necessity, introducibility through conservative inferential definitions), rather than systemic properties. MacFarlane, What does it mean to say that Logic is Formal?, p.17

The third (and most important) difference between pragmatic and principled demarcations has to do with the consequences one can draw for their verdicts about logicality. A demarcation tells us that this implication is a logical consequence, that one non-logical: but what follows from this classification? Not much, if the demarcation is pragmatic; potentially quite a bit, if the demarcation is principled. To see why, consider the significance of a demarcation of logic for the evaluation of logicism. What would be the upshot of showing that some significant part of mathematics is reducible to logic, where logic is given a pragmatic demarcation? We would have shown that the minimal conceptual apparatus that is significant for some purpose (say, deductive systematization of theories) already allows us to do a considerable amount of mathematics. Such a result would not be uninteresting, but it would not shed much light on traditional questions in the philosophy of mathematics (what is the source of objectivity of mathematics? does mathematics have special objects? how do we come by our mathematical knowledge?). If, on the other hand, we had a principled demarcation of logic, then a logical thesis would have clear philosophical significance: whatever privilege feature we use to pick out logic could be immediately transferred to the reduced body of mathematics. For example, if logical implication were demarcated in part by its necessity (in some sense), then the reduced body of mathematics would have been shown to be necessary (in the same sense). […] MacFarlane, What does it mean to say that Logic is Formal?, p.17-18

It seems to me that the philosophical projects that give point and purpose to demarcating logic in the first place require a principled rather than a pragmatic demarcation. The philosophical interest of projects like logicism depends on logicality having some philosophically interesting essence hence on logic being picked out by a distinguishing property or properties, not by its suitability for some task. […] Hence the focus of this investigation is on principled demarcations. MacFarlane, What does it mean to say that Logic is Formal?, p.19