Should tech companies send employees to conferences? My default answer is no.
Unless a company wants to promote itself and get more employees on board, not much happens during conferences that directly improves peoples' qualifications.
Most conferences comprise multiple presentations that introduce different topics. Speakers rarely dive into details to attract a broad range of listeners with a broad range of skills. Conferences are attended by large groups of people and it's very tough to explain complex topics during short talks. Even good speakers don't do it, because they'd confuse most of their audience.
Plus, presentations usually last no more than an hour. A conference is not a place to learn, it's a place to discover. Maybe there's a new tool that the speaker built and wants to sensitize people to it or a project manager wants to talk about how he and his company switched to agile. Whatever the topic, the presentation will usually be shallow with a "see more details at X" conclusion. Its goal is to spark interest.
If the goal is for employees to really learn and those employees are hard to replace creatives and not production line workers on a high turnover rate position, I believe other solutions are more effective.
Ideally, employees will learn on their own, at their own pace and by ordering topics to learn in a way that's best for them. But people have different interests, motivations and resources at their disposal. That's why companies should very publicly encourage their employees to learn and improve during work hours and assume they won't work directly on projects full-time. Not as a formal rule, but it should be clear that the workplace cares for employees' improvement.
It requires a level of trust from a company to do so. Chances are some employees will waste an excessive amount of time they're given on Facebook or watching YouTube videos - stuff totally unrelated to their work. But that's ok, because these employees are not right for the company anyway. If they can't take responsibility and use their time well, they should be let go.
Professional workshops are also a decent choice. But they have the same downside which causes parents to hire private tutors for their kids and send kids to private schools. The smaller the group, the more time a teacher will spend with a student and address areas challenging for that particular student. So make sure the workshop involves only a small group of employees in the company or create multiple groups. Professional teachers usually enforce an upper limit of students for a class also, because they know, from experience, how many they can handle at once.
Time for learning or doing workshops should be paid for. First, these replace conferences which would happen during work hours too. Second, they direct employees towards fulfilling the goals of the company better than before. Employees tend to learn things mutually beneficial for them and their company, like a new framework or how to test source code better.
An employer can't force after hours activities upon employees. But he can influence what they learn at work by awakening group responsibility for the company in them.
Employees will feel better and more up to date with the latest technologies, enjoy and connect with a company that gives them room to improve. It sounds far-fetched, but one thing I learned after multiple years of working in IT, is that the best employees love the hustle and want to improve. A win-win for everyone.