No question about it: When choosing analog components, designers have a huge array of options out there. For example, there are tens of thousands of op amps, many optimized for a specific application, and each offering a subtle combination of trade-offs in various primary, secondary, and even tertiary characteristics. At the end of the day, they are all op amps offering a basic function, despite the various implementations.
But signal isolation is a different sort of design challenge. (“Isolation” means there is no galvanic or ohmic path between input and output, yet energy representing a signal can pass through the barrier.) Isolation may be needed for a variety of reasons. These include maintaining overall signal integrity, providing common-mode rejection, ensuring user or component safety, separating “grounds” and circuit-common return paths, allowing ground-referenced digital outputs to drive floating MOSFET gates, enabling single-ended to differential signal conversion, and eliminating ground loops — and the list could go on much longer. In some cases, isolation's role is to improve performance. In others it is absolutely essential to meeting specs and having viable circuit.
But how best to achieve that isolation? That's the interesting part, since there are many fundamentally different ways to do it. The most common approaches use transformer (magnetic), optical, capacitive, and even RF-coupled techniques. Further complicating the situation, there are subsets within these topologies. For example, you can isolate a sensor signal via all-analog techniques. Otherwise you may choose to amplify and digitize it first (and you'll need isolated power, too), then just isolate the digitized serial bit stream and, if needed, reconvert to analog at the other end. Further, there are very different physical realizations ranging from monolithic ICs to hybrids and even modules.
Each of the very different approaches offers interesting and complex tradeoffs in speed, isolation voltage, bandwidth, footprint, long-term reliability, and cost. The vendor community is also quite diverse. Some sources offer only one approach and are therefore biased towards it, while others offer several types, and can give (in theory) a more even-handed assessment of the pros, cons, attributes, and trade-offs of isolation technique A versus B.
If I were interviewing a candidate for an analog circuit-design position (and thankfully, I'm not!), I would certainly ask him or her about a basic analog circuit, such as an op amp circuit with gain, of course. But for a position which requires a more experienced engineer, I'd ask about isolation, because it highlights the multiple, non-overlapping ways that you can achieve a given goal, and the trade-offs you make as you decide which approach best matches the target specifications. An engineer who understands the how and why of that, and can articulate it, is certainly a viable candidate.
What's your preferred isolation technique, and why? Do you ask analog job candidates about it?