Even when I've ended up needing a lawyer (albeit for private legal transactions like estate planning) going through the process of finding a template, customizing it to what I wanted, and thinking through as much as I could was invaluable. The subject matter can be complex and lawyers are expensive, paid by time, and (in my experience) have a habit of bulldozing through explanations to clients; the more prep you've done ahead of time the more value you can get out of your lawyer time (e.g. by knowing what questions to ask and having a clear picture of the issues at hand).

It is definitely possible. But it is not always trivial to know which solution you need without the advice of a lawyer. Lawyers use templates a lot, but they also know which templates work in which scenarios and in which jurisdictions.

Personally I'd be more comfortable using templates on my own for generic business documents, and less comfortable using them for areas of the law that vary greatly by state, like landlord/tenant law, or employment law.

You have a point, but it's important to note that the template needs to be local to you. Laws aren't global, what is an appropriate T&C for a service hosted in USA won't be okay for a service hosted in UK or Singapore, and even within USA differences in state laws sometimes are critical, so you need to ensure that you're not getting a template aimed at somewhere else.